Communication control method, user terminal, and communication apparatus

ABSTRACT

A communication control method comprises: receiving, by a user terminal, from a base station, first information indicating a Device to Device (D2D) frequency available in a D2D discovery procedure for discovering a proximal terminal; and using, by the user terminal, not only the frequency indicated by the first information, but also a frequency not indicated by the first information. The frequency not indicated by the first information is different from the frequency indicated by the first information and is indicated by second information received from another cell different from a cell in which the user terminal exists.

RELATED APPLICATIONS

This application is a Continuation application of U.S. patentapplication Ser. No. 15/077,084 filed Mar. 22, 2016, which is acontinuation application of international application PCT/JP2014/077146,filed Oct. 10, 2014, which claims benefit of JP Patent Application2013-213560, filed Oct. 11, 2013, JP Patent Application 2014-034211,filed Feb. 25, 2014, JP Patent Application 2014-034215, filed Feb. 25,2014, JP Patent Application 2014-059277, filed Mar. 20, 2014, and U.S.Provisional Application 62/056,105, filed Sep. 26, 2014, the entirety ofall applications hereby expressly incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a communication control method thatsupports D2D proximity service, a user terminal thereof, and acommunication apparatus thereof.

BACKGROUND ART

In 3GPP (3rd Generation Partnership Project) which is a project aimingto standardize a mobile communication system, the introduction of Deviceto Device (D2D) communication is discussed as a new function afterRelease 12 (see Non Patent Document 1.)

The D2D proximity service (D2D ProSe) is a service enabling directdevice-to-device communication within a synchronization cluster formedby a plurality of synchronized user terminals. The D2D proximity serviceincludes a D2D discovery procedure (Discovery) in which a proximalterminal is discovered and D2D communication (Communication) that isdirect device-to-device communication.

PRIOR ART DOCUMENT Non-Patent Document

-   Non Patent Document 1: 3GPP technical report “TR 22.803 V12.2.0”    June, 2013

SUMMARY

A communication control method comprises receiving, by a user terminal,from a base station in a serving cell of a first Public Land MobileNetwork (PLMN), first information including information of availableradio resources for directly receiving, by the user terminal, adiscovery signal in a frequency of the serving cell; receiving, by theuser terminal, second information transmitted by a System InformationBlock (SIB) from another base station in another cell having anotherfrequency different from the frequency of the serving cell, wherein thesecond information indicates available radio resources for directlyreceiving, by the user terminal, a discovery signal from another userterminal in the other frequency of the other cell of a second PLMNdifferent from the first PLMN; transmitting, by the user terminal, thesecond information received from the other base station, to the basestation in the serving cell; and directly receiving, by the userterminal, the discovery signal from the other user terminal existing inthe other cell, by using the available radio resources in the secondinformation.

A user terminal comprises a receiver configured to: receive, from a basestation in a serving cell of a first Public Land Mobile Network (PLMN),first information including information of available radio resources fordirectly receiving, by the user terminal, a discovery signal in afrequency of the serving cell, receive, from another base station inanother cell having another frequency different from the frequency ofthe serving cell, second information transmitted by a System InformationBlock (SIB), wherein the second information indicates available radioresources for directly receiving, by the user terminal, a discoverysignal from another user terminal in the other frequency of the othercell of a second PLMN different from the first PLMN, and directlyreceive the discovery signal from the other user terminal existing inthe other cell, by using the available radio resources in the secondinformation; and a transmitter configured to transmit the secondinformation received from the other base station, to the base station inthe serving cell.

A processor, communicatively coupled to a memory including a program,wherein the processor is configured to control the user terminal, and toexecute the program stored in the memory to perform processes of:receiving, from a base station in a serving cell of a first Public LandMobile Network (PLMN), first information including information ofavailable radio resources for directly receiving, by the user terminal,a discovery signal in a frequency of the serving cell; receiving, fromanother base station in another cell having another frequency differentfrom the frequency of the serving cell, second information transmittedby a System Information Block (SIB), wherein the second informationindicates available radio resources for directly receiving, by the userterminal, a discovery signal from another user terminal in the otherfrequency of the other cell of a second PLMN different from the firstPLMN; transmitting the second information received from the other basestation, to the base station in the serving cell; and directly receivingthe discovery signal from the other user terminal existing in the othercell, on a basis of the second information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an LTE system according toembodiments.

FIG. 2 is a block diagram of a UE according to the embodiments.

FIG. 3 is a block diagram of an eNB according to the embodiments.

FIG. 4 is a protocol stack diagram of a radio interface according to theembodiments.

FIG. 5 is a configuration diagram of a radio frame according to theembodiments.

FIG. 6 is a diagram for illustrating the D2D communication according tothe embodiments.

FIG. 7 is a diagram for describing an operation according to theembodiment.

FIG. 8 is a diagram for describing a D2D resource notification accordingto the embodiment.

FIG. 9 is a diagram for describing an operation according to anotherembodiment.

FIG. 10 is a diagram showing an operation environment according to theembodiment.

FIG. 11 is a sequence chart for describing a first operation accordingto the embodiment.

FIG. 12 is a sequence chart for describing a second operation accordingto the embodiment.

FIG. 13 is a sequence chart for describing a first modification of thesecond operation according to the embodiment.

FIG. 14 is a sequence chart for describing a second modification of thesecond operation according to the embodiment.

FIG. 15 is a sequence chart for describing a third modification of thesecond operation according to the embodiment.

FIG. 16 is a diagram showing an operation environment according toanother embodiment.

FIG. 17 is a sequence chart for describing a first method according tothe other embodiment.

FIG. 18 is a sequence chart for describing a second method according tothe other embodiment.

FIG. 19 is a sequence chart for describing a fourth method according tothe other embodiment.

FIG. 20 is a sequence chart for describing a fifth method according tothe other embodiment.

FIG. 21 is a diagram showing one example of an operation environmentaccording to another embodiment.

FIG. 22 is a diagram showing a case of monitoring UE camped on non-ProSesupported cell.

FIG. 23 is a diagram showing discovery monitoring without cellreselection.

DESCRIPTION OF THE EMBODIMENT Overview of Embodiment

Incidentally, in order to avoid interference between cellularcommunication and transmission and reception of a D2D radio signal byusing a D2D proximity service such as D2D communication, it is assumedthat the D2D proximity service is used under the management of acommunication apparatus such as a base station.

For example, in a cell in which a user terminal exists, a radio resource(D2D radio resource) available for D2D communication is reserved fromamong frequency bands to which the cell belongs to notify the userterminal of the D2D radio resource.

However, such a method has a problem in that when the D2D radio resourceis reserved, the radio resources available for the cellularcommunication relatively reduce.

A communication control method according to an embodiment comprises:receiving, by a user terminal, from a base station, first informationindicating a Device to Device (D2D) frequency available in a D2Ddiscovery procedure for discovering a proximal terminal; and using, bythe user terminal, not only the frequency indicated by the firstinformation, but also a frequency not indicated by the firstinformation. The frequency not indicated by the first information isdifferent from the frequency indicated by the first information and isindicated by second information received from another cell differentfrom a cell in which the user terminal exists.

The frequency indicated by the first information may be a frequency usedfor receiving a D2D discovery signal in the D2D discovery procedure.

A user terminal according to an embodiment comprises: a receiverconfigured to receive, from a base station, first information indicatinga Device to Device (D2D) frequency available in a D2D discoveryprocedure for discovering a proximal terminal; and a controllerconfigured to use, in the D2D discovery procedure, not only thefrequency indicated by the first information, but also a frequency notindicated by the first information. The frequency not indicated by thefirst information is different from the frequency indicated by the firstinformation and is indicated by second information received from anothercell different from a cell in which the user terminal exists.

A processor of a user terminal according to an embodiment configured to:receive, from a base station, first information indicating a Device toDevice (D2D) frequency available in a D2D discovery procedure fordiscovering a proximal terminal; and use, in the D2D discoveryprocedure, not only the frequency indicated by the first information,but also a frequency not indicated by the first information. Thefrequency not indicated by the first information is different from thefrequency indicated by the first information and is indicated by secondinformation received from another cell different from a cell in whichthe user terminal exists.

First Embodiment

Hereinafter, a first embodiment in which the present disclosure appliesto the LTE system will be described.

(System Configuration)

FIG. 1 is a configuration diagram of an LTE system according to thefirst present embodiment. As illustrated in FIG. 1, the LTE systemaccording to the first embodiment comprises UEs (User Equipments) 100,E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 10, and EPC(Evolved Packet Core) 20.

The UE 100 corresponds to the user terminal. The UE 100 is a mobilecommunication apparatus and performs radio communication with a cell (aserving cell) for a connection destination. Configuration of UE 100 willbe described later.

The E-UTRAN 10 corresponds to a radio access network. The E-UTRAN 10includes a plurality of eNBs 200 (evolved Node-Bs). The eNB 200corresponds to a base station. The eNBs 200 are connected mutually viaan X2 interface. Configuration of eNB 200 will be described later.

The eNB 200 manages one cell or a plurality of cells and performs radiocommunication with the UE 100 that establishes a connection with thecell. The eNB 200 has a radio resource management (RRM) function, arouting function of user data, and a measurement control function formobility control and scheduling and the like. It is noted that the“cell” is used as a term indicating a minimum unit of a radiocommunication area, and is also used as a term indicating a frequencyband or a function of performing radio communication with the UE 100.

The EPC 20 corresponds to a core network. The E-UTRAN 10 and the EPC 20constitute a network of the LTE system. The EPC 20 includes MMEs(Mobility Management Entities)/S-GWs (Serving-Gateways) 300 and an OAM(Operation and Maintenance) 400. The MME performs various mobilitycontrols and the like, for the UE 100. The S-GW performs transfercontrol of user data. The eNB 200 is connected to the MME/S-GW 300 viaan S1 interface. The OAM 400 is a server device managed by an operatorand performs maintenance and monitoring of the E-UTRAN 10.

FIG. 2 is a block diagram of the UE 100. As illustrated in FIG. 2, theUE 100 comprises an antenna 101, a radio transceiver 110, a userinterface 120, a GNSS (Global Navigation Satellite System) receiver 130,a battery 140, a memory 150, and a processor 160. The memory 150 and theprocessor 160 constitute a controller. The UE 100 may not have the GNSSreceiver 130. Furthermore, the memory 150 may be integrally formed withthe processor 160, and this set (that is, a chipset) may be called aprocessor 160′.

The antennas 101 and the radio transceiver 110 are used to transmit andreceive a radio signal. The radio transceiver 110 converts a basebandsignal (transmitted signal) output from the processor 160 into the radiosignal, and transmits the radio signal from the antennas 101.Furthermore, the radio transceiver 110 converts the radio signalreceived by the antennas 101 into the baseband signal (received signal),and outputs the baseband signal to the processor 160.

The user interface 120 is an interface with a user carrying the UE 100,and includes, for example, a display, a microphone, a speaker, variousbuttons and the like. The user interface 120 receives an operation froma user and outputs a signal indicating the content of the operation tothe processor 160. The GNSS receiver 130 receives a GNSS signal in orderto obtain location information indicating a geographical location of theUE 100, and outputs the received signal to the processor 160. Thebattery 140 accumulates a power to be supplied to each block of the UE100.

The memory 150 stores a program to be executed by the processor 160 andinformation to be used for a process by the processor 160. The processor160 includes a baseband processor that performs modulation anddemodulation, encoding and decoding and the like of the baseband signal,and a CPU (Central Processing Unit) that performs various processes byexecuting the program stored in the memory 150. The processor 160 mayfurther include a codec that performs encoding and decoding of sound andvideo signals. The processor 160 implements various processes andvarious communication protocols described later.

FIG. 3 is a block diagram of the eNB 200. As illustrated in FIG. 3, theeNB 200 comprises an antenna 201, a radio transceiver 210, a networkinterface 220, a memory 230, and a processor 240. The memory 230 and theprocessor 240 constitute a controller. It is noted that the memory 230may be integrally formed with the processor 240, and this set (that is,a chipset) may be called a processor.

The antenna 201 and the radio transceiver 210 are used to transmit andreceive a radio signal. The radio transceiver 210 converts the basebandsignal (transmitted signal) output from the processor 240 into the radiosignal, and transmits the radio signal from the antenna 201.Furthermore, the radio transceiver 210 converts the radio signalreceived by the antenna 201 into the baseband signal (received signal),and outputs the baseband signal to the processor 240.

The network interface 220 is connected to the neighboring eNB 200 viathe X2 interface and is connected to the MME/S-GW 300 via the S1interface. The network interface 220 is used in communication performedon the X2 interface and communication performed on the S1 interface.

The memory 230 stores a program to be executed by the processor 240 andinformation to be used for a process by the processor 240. The processor240 includes the baseband processor that performs modulation anddemodulation, encoding and decoding and the like of the baseband signaland a CPU that performs various processes by executing the programstored in the memory 230. The processor 240 implements various processesand various communication protocols described later.

FIG. 4 is a protocol stack diagram of a radio interface in the LTEsystem. As illustrated in FIG. 4, the radio interface protocol isclassified into a layer 1 to a layer 3 of an OSI reference model,wherein the layer 1 is a physical (PHY) layer. The layer 2 includes aMAC (Medium Access Control) layer, an RLC (Radio Link Control) layer,and a PDCP (Packet Data Convergence Protocol) layer. The layer 3includes an RRC (Radio Resource Control) layer.

The PHY layer performs encoding and decoding, modulation anddemodulation, antenna mapping and demapping, and resource mapping anddemapping. Between the PHY layer of the UE 100 and the PHY layer of theeNB 200, user data and control signal are transmitted through thephysical channel.

The MAC layer performs preferential control of data, and aretransmission process and the like by hybrid ARQ (HARQ). Between theMAC layer of the UE 100 and the MAC layer of the eNB 200, user data andcontrol signal are transmitted via a transport channel. The MAC layer ofthe eNB 200 includes a scheduler for determining (scheduling) atransport format of an uplink and a downlink (a transport block size, amodulation and coding scheme) and a resource block to be assigned to theUE 100.

The RLC layer transmits data to an RLC layer of a reception side byusing the functions of the MAC layer and the PHY layer. Between the RLClayer of the UE 100 and the RLC layer of the eNB 200, user data andcontrol signal are transmitted via a logical channel.

The PDCP layer performs header compression and decompression, andencryption and decryption.

The RRC layer is defined only in a control plane which treats thecontrol signal. Between the RRC layer of the UE 100 and the RRC layer ofthe eNB 200, a control signal (an RRC message) for various types ofconfigurations is transmitted. The RRC layer controls the logicalchannel, the transport channel, and the physical channel in response toestablishment, re-establishment, and release of a radio bearer. When aconnection (an RRC connection) is established between the RRC of the UE100 and the RRC of the eNB 200, the UE 100 is in a connected state (aRRC connection state), and when the RRC connection is not established,the UE 100 is in an idle state (a RRC idle state).

A NAS (Non-Access Stratum) layer positioned above the RRC layer performssession management and mobility management, for example.

FIG. 5 is a configuration diagram of a radio frame used in the LTEsystem. In the LTE system, OFDMA (Orthogonal Frequency Division MultipleAccess) is applied in a downlink (DL), and SC-FDMA (Single CarrierFrequency Division Multiple Access) is applied in an uplink (UL),respectively.

As illustrated in FIG. 5, the radio frame (system frame) is configuredby 10 subframes arranged in a time direction, wherein each subframe isconfigured by two slots arranged in the time direction. Each subframehas a length of 1 ms and each slot has a length of 0.5 ms. Each slotincludes a plurality of resource blocks (RBs) in a frequency direction,and a plurality of symbols in the time direction. Each resource blockincludes a plurality of subcarriers in the frequency direction. A radioresource unit is configured by one subcarrier and one symbol.

Among radio resources assigned to the UE 100, a frequency resource canbe configured by a resource block and a time resource can be configuredby a subframe (or slot).

In the downlink, an interval of several symbols at the head of eachsubframe is a region mainly used as a physical downlink control channel(PDCCH) for transmission of a downlink control signal. Furthermore, theremaining part of each subframe is a region mainly used as a physicaldownlink shared channel (PDSCH) for transmission of a downlink userdata.

In the uplink, both end portions in the frequency direction of eachsubframe are regions mainly used as a physical uplink control channel(PUCCH) for transmission of an uplink control signal. Furthermore, thecenter portion in the frequency direction of each subframe is a regionthat can be mainly used as a physical uplink shared channel (PUSCH) fortransmission of an uplink user data.

(D2D Proximity Service)

A D2D proximity service will be described, below. An LIE systemaccording to the first embodiment supports the D2D proximity service.The D2D proximity service is described in Non Patent Document 1. Anoutline thereof will be presented here.

The D2D proximity service (D2D ProSe) is a service enabling a directUE-to-UE communication within a synchronization cluster formed by aplurality of synchronized UEs 100. The D2D proximity service includes aD2D discovery procedure (Discovery) in which a proximal UE is discoveredand D2D communication (Communication) that is direct UE-to-UEcommunication. The D2D communication is also called DirectCommunication.

A scenario in which all the UEs 100 forming the synchronization clusterare located inside a cell coverage is called “In coverage”. A scenarioin which all the UEs 100 forming the synchronization cluster are locatedoutside the cell coverage is called “Out of coverage”. A scenario inwhich some UEs 100 in the synchronization cluster are located in thecell coverage and the remaining UEs 100 are located outside the cellcoverage is called “Partial coverage”.

In coverage, an eNB 200 is a D2D synchronization source, for example. AD2D asynchronization source, from which a D2D synchronization signal isnot transmitted, is synchronized with the D2D synchronization source.The eNB 200 that is a D2D synchronization source transmits, by abroadcast signal, D2D resource information relating to a D2D radioresource available for the D2D proximity service, as a D2D resourcenotification. The D2D resource information includes informationindicating a radio resource available for the D2D discovery procedure(Discovery resource information) and information indicating a radioresource available for the D2D communication (Communication resourceinformation), for example. The UE 100 that is a D2D asynchronizationsource performs the D2D discovery procedure and the D2D communication onthe basis of the D2D resource information received from the eNB 200.

Out of coverage or in Partial coverage, the UE 100 is the D2Dsynchronization source, for example Out of coverage, the UE 100 that isa D2D synchronization source transmits the D2D resource informationindicating a radio resource available for the D2D proximity service, bya D2D synchronization signal, for example The D2D synchronization signalis a signal transmitted in the D2D synchronization procedure in which adevice-to-device synchronization is established. The D2D synchronizationsignal includes D2DSS and a physical D2D synchronization channel(PD2DSCH). The D2DSS is a signal for providing a synchronizationreference of a time and a frequency. The PD2DSCH is a physical channelthrough which more information can be conveyed than the D2DSS. ThePD2DSCH conveys the above-described D2D resource information (theDiscovery resource information and the Communication resourceinformation). Alternatively, when the D2DSS is associated with the D2Dresource information, the PD2DSCH may be rendered unnecessary.

The D2D discovery procedure is used mainly when the D2D communication isperformed by unicast. One UE 100 uses any particular radio resource outof radio resources available for the D2D discovery procedure whenstarting the D2D communication with another UE 100 to transmit theDiscovery signal (D2D discovery signal). The other UE 100 scans theDiscovery signal within the radio resources available for the D2Ddiscovery procedure when starting the D2D communication with the one UE100 to receive the Discovery signal. The Discovery signal may includeinformation indicating a radio resource used by the one UE 100 for theD2D communication.

Next, the D2D communication is used as an example to proceed withdescription with a comparison between cellular communication that isordinary communication in the LTE system and radio communication in theD2D proximity service. FIG. 6 is a diagram for describing the D2Dproximity service (for example, the D2D communication) according to thefirst embodiment.

The cellular communication is a communication mode in which a data pathis made through a network (E-UTRAN 10, EPC 20). The data path is atransmission path for user data.

On the other hand, as shown in FIG. 6, the radio communication in theD2D proximity service is a communication mode in which a data path setbetween the UEs is made without a network. A D2D UE group formed by aplurality of UEs 100 (UE 100-1 and UE 100-2) adjacent to each otherdirectly performs radio communication with low transmission power. Asdescribed above, such a D2D UE group is a “cluster” (synchronizationcluster).

The UE 100-1 and the UE 100-2 are synchronized with each other. Each ofthe UE 100-1 and the UE 100-2 may recognize the other UE by a proximitydiscovery (Discovery) process. It is noted that in the first embodiment(and some of the other embodiments described later), the “Discoveryprocess” may be included in the “D2D communication”. That is, it shouldbe noted that the radio communication in the D2D proximity service(specifically, the radio communication in the D2D discovery procedure(Discovery) and the radio communication in the D2D communication(Communication)) may be generally called “D2D communication”.

A frequency band of the D2D communication may be used commonly with afrequency band of the cellular communication, or may be different fromthe frequency band of the cellular communication. Thus, when theplurality of proximity UEs 100 directly perform radio communication withlow transmission power, it becomes possible to reduce a powerconsumption of the UE 100 in comparison with in cellular communication.

In the first embodiment, as a mode of the D2D communication in a lowerlayer, broadcast is mainly assumed. For example, CSMA (Carrier SenseMultiple Access) is applied to the D2D communication. The D2Dcommunication performed by such a broadcast is especially suitablyapplied to public safety in a time of disaster or the like. It is notedthat the D2D communication can be applied to a group-cast (multicast) ora unicast by performing encryption or the like in an upper layer.

It is noted that the In coverage case includes an “Intra-cell” casewhere each UE 100 forming the synchronization cluster exists in the samecell and an “Inter-cell” case where each UE 100 forming thesynchronization cluster exists dispersively in a plurality of cells.

(Operation According to First Embodiment)

FIG. 7 is a diagram for describing an operation according to the firstembodiment. FIG. 8 is a diagram for describing a D2D resourcenotification according to the first embodiment.

As shown in FIG. 7, a plurality of cells belonging to respectivelydifferent frequency bands is arranged. An eNB 200-1 manages a cell #1belonging to a 2-GHz band and a cell #2 belonging to an 800-MHz band. AneNB 200-2 manages a cell #3 belonging to a 1.7-GHz band. An eNB 200-3manages a cell #4 belonging to a 3.5-GHz band. The cell #4 is a smallcell (for example, a pico cell or a femto cell) arranged inside the cell#3. For example, the 800-MHz band, the 1.7-GHz band, the 2-GHz band, andthe 3.5-GHz band are operator bands assigned to the same operator. Eachof the 800-MHz band, the 1.7-GHz band, the 2-GHz band, and the 3.5-GHzband may be used as a component carrier in a carrier aggregation. Eachof the component carriers includes a plurality of resource blocks in afrequency direction.

In the cell #2, a plurality of UEs 100 exists. The cell #2 is a servingcell of the UEs 100. The UEs 100 may be in an RRC connected state in thecell #2, and in an RRC idle state in the cell #2. The UE 100-1 of theplurality of UEs 100 is located inside a region where the cell #2 andthe cell #3 overlap and near the cell #1. The UE 100 wishes to start theD2D communication, or is performing the D2D communication.

When the D2D communication in such In coverage is assumed, the D2Dcommunication may be performed under the management of the eNB 200 inorder to avoid interference between the D2D communication and thecellular communication. For example, the eNB 200-1 reserves a D2D radioresource (a resource block, a subframe, etc.) available for the D2Dcommunication, out of the 800-MHz band to which the cell #2 belongs, andnotifies the UE 100 of the D2D radio resource. However, in such amethod, the radio resources available for the cellular communicationrelatively reduce due to reserving the D2D radio resource.

Therefore, in the first embodiment, when the frequency band differentfrom the 800-MHz band to which the cell #2 belongs is made available forthe UE 100-1 and the UE 100-2 to use for the D2D communication, itbecomes possible to perform the D2D communication without reducing theradio resources available for the cellular communication.

A communication control method according to the first embodimentcomprises: a transmission step of transmitting, by the eNB 200-1configured to use the 800-MHz band for the cellular communication, atleast one D2D resource notification (Resource indication for D2D) in the800-MHz band; and a reception step of receiving, by the UE 100, the D2Dresource notification transmitted in the 800-MHz band. In the firstembodiment, the 800-MHz band corresponds to a predetermined frequencyband. The eNB 200-1 corresponds to a communication apparatus configuredto use the predetermined frequency band. In the following description,description proceeds with a focus on the D2D resource notificationtransmitted by the eNB 200-1 in the 800-MHz band.

The D2D resource notification (D2D resource information) includesinformation indicating the D2D frequency band that is a frequency bandavailable for the D2D communication. In the first embodiment, the D2Dfrequency band is a frequency band different from the 800-MHz band. Inan operation environment shown in FIG. 7, the cell #4 belonging to the3.5-GHz band is located far from the cell #2 belonging to the 800-MHzband, and thus, in view of avoiding interference, it is preferable thatthe D2D frequency band in the cell #2 is a 3.5-GHz band.

On the other hand, the cell #1 belonging to the 2-GHz band is located inthe cell #2, and thus, in view of avoiding interference, it is notpreferable that the D2D frequency band in the cell #2 is a 2-GHz band.Further, the cell #3 belonging to the 1.7-GHz band neighbors the cell#2, and thus, in view of avoiding interference, it is not preferablethat the D2D frequency band in the cell #2 is a 1.7-GHz band. However,although the description is given in detail later, as long as apredetermined condition to avoid interference is satisfied, the 1.7-GHzband and the 2-GHz band may be made available in the cell #2 for the D2Dcommunication.

It is noted that the eNB 200-1 performs base-station-to-base-stationcommunication with neighboring eNBs (the eNB 200-2 and the eNB 200-3) tothereby determine the D2D frequency band. Alternatively, the D2Dfrequency band determined by the EPC 20 may be notified and set to theeNB 200-1.

In the first embodiment, the eNB 200-1 includes the informationindicating the D2D frequency band, into the D2D resource notification,as long as the D2D frequency band is a frequency band different from the800-MHz band. That is, when the 800-MHz band is the D2D frequency band,the eNB 200-1 may not include the information indicating the D2Dfrequency band into the D2D resource notification.

In the first embodiment, the eNB 200-1 transmits the D2D resourcenotification by broadcast in the 800-MHz band. The UE 100 receives theD2D resource notification transmitted by broadcast in the 800-MHz band.For example, the D2D resource notification may be an information elementof an SIB (System Information Block) that is an RRC message common toall the UEs in the cell #2. When the D2D resource notification istransmitted by the SIB, it becomes possible even for the UE 100 in anRRC idle state to acquire the D2D resource notification. However, it isnot limited to transmitting the D2D resource notification by broadcast,and it may be possible to transmit the D2D resource notification byunicast to the UE 100 in an RRC connected state.

As shown in FIG. 8, the information indicating the D2D frequency bandincludes information I1 indicating a center frequency of the D2Dfrequency band, and information I2 indicating a bandwidth of the D2Dfrequency band. The information I2 is the number of resource blockscorresponding to a bandwidth in a D2D frequency band, for example.

Further, the D2D resource notification (D2D resource information) mayinclude the information indicating a D2D radio resource that is a radioresource available for the D2D communication, out of a plurality ofradio resources corresponding to the D2D frequency band. The informationindicating a D2D radio resource is information I3 indicating a resourceblock configuring the D2D radio resource. The information I3 is aresource block number, for example. The information indicating a D2Dradio resource may be information I6 indicating a subframe configuringthe D2D radio resource. The information I6 is a subframe number, forexample.

The D2D resource notification (D2D resource information) may include atransmission power control parameter 14 applied to D2D communicationthat uses the D2D frequency band and/or the D2D radio resource. Thetransmission power control parameter 14 is a maximum transmission power“PMax” of the D2D communication, for example. The UE 100 determines theD2D transmission power “P” by the following calculating formula:

P=Min(PMax,Min(IMax+PLCell,PO_Nominal_D2D+αPLD2D))

“IMax” denotes restriction on interference to a cell, “PLCell” denotes apath loss with a cell, “PO_Nominal_D2D” denotes D2D transmission powerthat serves as a base, “α” denotes a path loss compensation factor, and“PLD2D” denotes a path loss with a D2D communication partner. When theabove-described calculating formula is used, the transmission powercontrol parameter 14 may include “IMax”, “PO_Nominal_D2D”, and “α”. Itis noted that “PO_Nominal_D2D” may be a value unique to a UE.

However, it is not limited that the D2D radio resource and/or the D2Dtransmission power implicitly may be indicated in the D2D resourcenotification. The D2D radio resource and/or the D2D transmission powermay be implicitly indicated. In this case, the D2D resource notificationmay include information I5 indicating a use case where the D2D frequencyband (and/or the D2D radio resource) is used for the D2D communication.The use case is associated with a transmission power control parameterapplied to the D2D communication, and/or the D2D radio resource that isa radio resource available for the D2D communication. For example, whenthe D2D radio resource is not designated in the D2D resourcenotification, the use case may be associated with the D2D radioresource. When the D2D transmission power control parameter is notdesignated in the D2D resource notification, the use case may beassociated with the D2D transmission power control parameter.

The use case is Commercial or Public safely. For example, a rule that“in Commercial, the maximum D2D transmission power is 23 dBm, and inPublic safety, the maximum D2D transmission power may exceed 23 dBm” ispreviously set to the UE 100, and the UE 100 controls the D2Dtransmission power in accordance with the rule. It is noted that each ofCommercial and Public safety may be further categorized.

Instead of the above-described rule, a rule that uses “UE power class”(see TS36.101) may be applied. For example, a rule that “in Publicsafety, UE power class 1 (31 dBm) is applied” may be used.

The D2D resource notification (D2D resource information) may includeinformation I7 indicating an available condition that is a conditionunder which a D2D frequency band is available. The UE 100 determines onthe basis of the information I7 indicating an available conditionwhether or not the D2D frequency band can be available for the D2Dcommunication.

The available condition is at least one of: search (for example, a cellsearch) for a D2D frequency band is not successful; and a measurementresult (for example, reference signal received power) for a D2Dfrequency band is worse than a threshold value. As a result, when theD2D frequency band indicated by the D2D resource notification may causeinterference, it is possible to ensure that the D2D frequency band isnot used for the D2D communication.

Alternatively, the available condition may be that a permission to usethe D2D frequency band is obtained from the eNB 200-1. In this case, theUE 100 transmits a report on the measurement result about the D2Dfrequency band, to the eNB 200-1. The eNB 200-1 determines on the basisof the report whether or not a permission to use the D2D frequency bandis applied to the UE 100. As a result, when the D2D frequency bandindicated by the D2D resource notification may cause interference, it ispossible to ensure that the D2D frequency band is not used for the D2Dcommunication.

The D2D resource notification (D2D resource information) may includeinformation I8 for designating a synchronization target that is to beused as a reference (hereinafter, “D2D synchronization reference”) of atime synchronization and/or a frequency synchronization in a process forthe D2D communication. The process for the D2D communication includes aDiscovery process, a D2D transmission process, and a D2D receptionprocess, for example. The information I8 includes information indicatinga frequency band that is to be used as the D2D synchronizationreference, or a cell identifier of a cell that is to be used as the D2Dsynchronization reference, for example. The UE 100 uses the designatedsynchronization target (the frequency band or the cell) as the D2Dsynchronization reference. As a result, when a plurality of UEs 100receive the D2D resource notifications from different cells, if the D2Dresource notification is configured such that each of the D2D frequencyband and the D2D synchronization reference is unified, then it becomespossible to perform the D2D communication of the Inter-cell by theplurality of UEs 100.

However, the information I8 may not be necessarily included in the D2Dresource notification. In this case, the UE 100 uses a transmissionsource (the frequency band or the cell) of the D2D resource notificationas the D2D synchronization reference.

Summary of First Embodiment

As described above, the communication control method according to thefirst embodiment comprises: a transmission step of transmitting, by theeNB 200-1 configured to use a predetermined frequency band for cellularcommunication, at least one D2D resource notification in thepredetermined frequency band; and a reception step of receiving, by theUE 100, the D2D resource notification transmitted in the predeterminedfrequency band. The D2D resource notification includes the informationindicating the D2D frequency band that is a frequency band available forthe D2D communication. As a result, the frequency band different from tthe predetermined frequency can be made available to use for the D2Dcommunication. Thus, it becomes possible to perform the D2Dcommunication without reducing the radio resources available for thecellular communication.

Modification of First Embodiment

The D2D resource notification may include at least one item of thefollowing information in addition to the above-described information.

Configuration of the Discovery Subframe

The Discovery subframe is a subframe used for the Discovery process. TheConfiguration of the Discovery subframe is a list of system framenumbers and subframe numbers used for the Discovery process, forexample. Alternatively, the Configuration of the Discovery subframe maybe a cycle and a period in which the Discovery subframe is arranged.

Configuration of Discovery Signal

The Discovery signal is a radio signal for the Discovery processtransmitted and received in the Discovery process. The Configuration ofthe Discovery signal is the number of resource blocks used fortransmitting the Discovery signal, and a parameter for determining ahopping pattern in time/frequency/power directions, for example.

Configuration of Resource Block for D2D Control Channel

The D2D control channel is a control channel between the UEs. TheConfiguration of a resource block for the D2D control channel is aresource block number corresponding to the D2D control channel, forexample.

Method of Controlling to Transmit Discovery Signal

A method of controlling to transmit the Discovery signal is either oneof a full control by a network or a cluster head, or CSMA.

Method of Controlling to Transmit Communication Signal

The Communication signal is a radio signal transmitted and received inthe D2D communication, and mainly is a user data signal. A method ofcontrolling to transmit the Communication signal is either one of a fullcontrol by a network or a cluster head, or CSMA.

Second Embodiment

Next, the second embodiment will be described. Description proceeds witha focus on a difference from the above-described first embodiment, andthe configuration similar to that of the first embodiment will not bedescribed.

In the first embodiment, by using, for the D2D communication, thefrequency band different from a predetermined frequency band used forthe cellular communication, the D2D communication is enabled withoutreducing the radio resources available for the cellular communication.In the second embodiment, by using, for the D2D communication, afrequency band in another PLMN (Public Land Mobile Network), the D2Dcommunication is enabled without reducing the radio resources availablefor the cellular communication.

Further, a case is assumed where the UE 100-1 and the UE 100-2 exist indifferent cells. In this case, there is a possibility that between acell in which the UE 100-1 exists (first cell) and a cell in which theUE 100-2 exists (second cell), a time-frequency resource (D2D radioresource) available for a D2D proximity service (for example, a D2Ddiscovery procedure and D2D communication) differ. As a result, it isnot possible to start the D2D communication between the UEs existing inthe different cells, and it may thus not be possible to use the D2Dproximity service.

Therefore, in the second embodiment, an operation for enabling use ofthe D2D proximity service between the UEs existing in the differentcells will also be described.

(Operation According to Second Embodiment)

Hereinafter, an operation according to the second embodiment will bedescribed. FIG. 10 is a diagram showing an operation environmentaccording to the second embodiment.

As shown in FIG. 10, an eNB 200 #1 is included in a PLMN #1 that is anLTE network of a network operator #1. Therefore, the eNB #1 belongs tothe PLMN #1. To the PLMN #1, a frequency band #1 (Freq. #1) is assigned.The eNB 200 #1 manages a cell #1 of the frequency band #1. The cell #1belongs to the frequency band #1 and belongs to the PLMN #1.

A UE 100 #1 exists in the cell #1, and registers its location in thePLMN #1. That is, the UE 100 #1 belongs to the PLMN #1. For example, theUE 100 #1 is in an RRC idle state in the cell #1. Alternatively, the UE100 #1 may be in an RRC connected state in the cell #1.

An eNB 200 #2 is included in a PLMN #2 that is an LTE network of anetwork operator #2. Therefore, the eNB #2 belongs to the PLMN #2. Tothe PLMN #2, a frequency band #2 (Freq. #2) is assigned. The eNB 200 #2manages a cell #2 of the frequency band #2. The cell #2 belongs to thefrequency band #2 and belongs to the PLMN #2. The cell #2 is a celldifferent from the cell #1. In the present embodiment, the cell #2 islocated adjacent to the cell #1. The cell #2 may be neighbor, overlap,and be away from the cell #1. The eNB 200 #2 is synchronized with theeNB 200 #1. Alternatively, the eNB 200 #2 may also be asynchronized withthe eNB 200 #1.

The UE 100 #2 exists in the cell #2, and registers its location in thePLMN #2. That is, the UE 100 #2 belongs to the PLMN #2. The UE 100 #2 isin an RRC idle state in the cell #2. Alternatively, the UE 100 #2 may bein an RRC connected state in the cell #2.

In such an operation environment, a case is assumed where theabove-described D2D proximity service is applied to the UE 100 #1 andthe UE 100 #2 (that is, a case where the UE 100 #1 and the UE 100 #2 usethe D2D proximity service).

In such a case, the UE 100 #1 receives first D2D resource information(for example, the Discovery resource information and the Communicationresource information) from the eNB 200 #1. The first D2D resourceinformation is information on the D2D radio resource available for theD2D proximity service in the cell #1. Specifically, each item of theDiscovery resource information and the Communication resourceinformation transmitted by the eNB 200 #1 indicates a radio resourceincluded in the frequency band #1. The (first) D2D resource informationwill be described in detail later.

The UE 100 #2 receives second D2D resource information (for example, theDiscovery resource information and the Communication resourceinformation) from the eNB 200 #2. The second D2D resource information isinformation on the D2D radio resource available for the D2D proximityservice in the cell #2. Specifically, each item of the Discoveryresource information and the Communication resource informationtransmitted by the eNB 200 #2 indicates a radio resource included in thefrequency band #2.

The frequency band #1 used by the UE 100 #1 for the D2D discoveryprocedure/the D2D communication may not match the frequency band #2 usedby the UE 100 #2 for the D2D discovery procedure/the D2D communication,and thus, the D2D communication may not be started by the UE 100 #1 andthe UE 100 #2 belonging to different PLMNs.

Therefore, in the embodiment, the following operation enables startingthe D2D communication between user terminals belonging to the differentPLMNs.

(A) First Operation

A first operation will be described using FIG. 11. FIG. 11 is a sequencechart for describing the first operation according to the embodiment.

It is noted that description proceeds below with an assumption that theUE 100 #1 exists at a location where it is possible to receive a radiosignal from the eNB 200 #2 (cell #2) and the UE 100 #2 exists at alocation where it is possible to receive a radio signal from the eNB 200#1 (cell #1).

As shown in FIG. 11, in step S101, the eNB 200 #1 transmits, bybroadcast, a system information block (SIB) including the first D2Dresource information, into the cell #1. That is, the eNB 200 #1 uses theradio resource in the frequency band #1 to transmit, by broadcast, theSIB including the first D2D resource information. Likewise, the eNB 200#2 uses the radio resource in the frequency band #2 to transmit, bybroadcast, the SIB including the second D2D resource information, intothe cell #2. The SIBs correspond to a D2D resource notification.

The UE 100 #1 scans the frequency band different from the frequency band#1 operated in the PLMN #1 to which the cell #1 belongs. Specifically,the UE 100 #1 performs a cell search in the frequency band #2. The UE100 #1 discovers the cell #2 of the frequency band #2 by the cellsearch, and receives the SIB from the cell #2 (eNB 200 #2). On the otherhand, similarly to the UE 100 #1, the UE 100 #2 discovers the cell #1 ofthe frequency band #1 by the cell search, and receives the SIB from thecell #1 (eNB 200 #1).

In step S102, the UE 100 #1 decodes the SIB to decode the second D2Dresource information and reads a content of the second D2D resourceinformation. As a result, the UE 100 #1 receives (obtains) the secondD2D resource information. For example, the UE 100 #1 comprehends whetherthe D2D proximity service (D2D communication) is permitted in the cell#2 (frequency band #2). Therefore, the UE 100 #1 intercepts the radiosignal including the D2D resource information in another PLMN. On theother hand, similarly to the UE 100 #1, the UE 100 #2 reads the firstD2D resource information. As a result, the UE 100 #2 receives (obtains)the first D2D resource information.

In step S103, each of the UE 100 #1 and the UE 100 #2 performs the D2Dcommunication on the basis of the first D2D resource information and thesecond D2D resource information.

For example, the UE 100 #1 uses the frequency band #1 permitted in usein the PLMN #1 to transmit the D2D discovery signal. The UE 100 #2receives the D2D discovery signal transmitted by using the frequencyband #1, on the basis of the first D2D resource information. As aresult, the UE 100 #2 discovers the UE 100 #1. On the other hand, the UE100 #2 uses the frequency band #2 permitted in use in the PLMN #2 totransmit the D2D discovery signal (or a response to the D2D discoverysignal from the UE 100 #1). The UE 100 #1 receives the D2D discoverysignal from the UE 100 #2, on the basis of the second D2D resourceinformation. As a result, the UE 100 #1 and the UE 100 #2 are capable ofdiscovering a partner terminal that may be a communication partner ofthe D2D communication.

The UE 100 #1 and the UE 100 #2 that has discovered the partner terminalare capable of performing the D2D communication by an operation similarto the above-mentioned D2D discovery signal. As a result, the UE 100 #1and the UE 100 #2 are capable of performing the D2D communication in afrequency band permitted each in the PLMNs of the UE 100 #1 and the UE100 #2.

In accordance with the first operation, each UE 100 is capable ofobtaining the D2D resource information in a different PLMN, and thus,each UE 100 is capable of starting the D2D communication between theuser terminals belonging to the different PLMNs.

(B) Second Operation

Next, a second operation will be described using FIG. 12. FIG. 12 is asequence chart for describing the second operation according to theembodiment.

In the first operation, the UE 100 receives the D2D resource informationin another cell (another PLMN) from another eNB 200 (another cell)belonging to the other PLMN. In the second operation, the UE 100receives the D2D resource information in another cell, from a cell inwhich the UE 100 exist.

As shown in FIG. 12, in step S201, the eNB 200 #1 transmits (notifiesof) the first D2D resource information to the eNB 200 #2 via NW(network). Further, the eNB 200 #1 receives, via the NW, the second D2Dresource information from the eNB 200 #2. As a result, the eNB 200 #1and the eNB 200 #2 exchange and share the respective D2D resourceinformation. The eNB 200 #1 is capable of changing the configuration ofthe D2D resource of the eNB 200 #1 (that is, the first D2D resourceinformation), on the basis of the second D2D resource information. TheeNB 200 #2 is, similarly to the eNB 200 #1, capable of changingconfiguration of the D2D resource (that is, the second D2D resourceinformation), on the basis of the first D2D resource information. Thus,the eNB 200 #1 and the eNB 200 #2 cooperate on the D2D resource.

It is noted that the first D2D resource information includes frequencyresource information on the frequency band #1 available for the D2Dproximity service in the cell #1. Likewise, the second D2D resourceinformation includes frequency resource information on the frequencyband #2 available for the D2D proximity service in the cell #2.

Further, when the eNB 200 #1 holds an Inter-PLMN list regarding the D2Dresource information in another PLMN, the eNB 200 #1 may update theInter-PLMN list, on the basis of the second D2D resource informationfrom the eNB 200 #2. That is, the eNB 200 #1 may update the informationon the frequency band #2 available for the D2D proximity service in thecell #2, held by the eNB 200 #1, on the basis of the second D2D resourceinformation. The same is true of the eNB 200 #2.

In step S202, the eNB 200 #2 transmits, by broadcast, the SIB includingthe first D2D resource information, into the cell #2. The UE 100 #2receives the first D2D resource information. It is noted that the eNB200 #2 may transmit the SIB including the second D2D resourceinformation, in addition to the first D2D resource information.

In step S203, the eNB 200 #1 transmits the SIB including the second D2Dresource information, similarly to step S202. The UE 100 #1 receives thesecond D2D resource information.

In step S204, the UE 100 #1 starts monitoring the frequency band(frequency band #2) of the D2D resource available for the PLMN #2, onthe basis of the second D2D resource information received from the eNB200 #1. Specifically, the UE 100 #1 starts scanning the frequency band#2.

In step S205, the UE 100 #2 transmits the D2D radio signal, on the basisof the second D2D resource information. Specifically, the UE 100 #2 usesthe D2D resource of the frequency band #2 to transmit the D2D radiosignal. The UE 100 #1 that monitors the frequency band #2 receives theD2D radio signal from the UE 100 #2.

In step S206, the UE 100 #1 ends monitoring. When a predetermined periodpasses since starting monitoring or when a predetermined time reaches,the UE 100 #1 may end monitoring. When reception of the D2D radio signalis used as a trigger, the UE 100 #1 may end monitoring.

In step S207, the UE 100 #2 starts monitoring the frequency band(frequency band #1) of the D2D resource available for the PLMN #1, onthe basis of the first D2D resource information received from the eNB200 #2.

In step S208, the UE 100 #1 transmits the D2D radio signal, on the basisof the first D2D resource information. Specifically, the UE 100 #1 usesthe D2D resource of the frequency band #1 to transmit the D2D radiosignal. The D2D radio signal may be a response signal to the D2D radiosignal from the UE 100 #2.

The UE 100 #2 that monitors the frequency band #1 receives the D2D radiosignal from the UE 100 #1.

In step S209, the UE 100 #2 ends monitoring, similarly to step S206.

Each of the UE 100 #1 and the UE 100 #2 is capable of using the D2Dproximity service, on the basis of the received D2D radio signal.

In accordance with the second operation, even when the UE 100 is notcapable of scanning only the frequency band in the PLMN of the UE 100,the UE 100 is capable of acquiring the D2D resource information in adifferent PLMN. As a result, it becomes possible to start the D2Dcommunication between the user terminals belonging to the differentPLMNs.

(C) First Modification of Second Operation

Next, a first modification of the second operation will be described byusing FIG. 13. FIG. 13 is a sequence chart for describing the firstmodification of the second operation according to the second embodiment.

In the second operation, the eNB 200 voluntarily transmits the D2Dresource information in another PLMN, to the UE 100. In the firstmodification of the second operation example, the D2D resourceinformation is transmitted in response to a request from the UE 100.

As shown in FIG. 13, step S301 corresponds to step S201.

In step S302, the UE 100 #1 becomes capable of using the D2D proximityservice. Specifically, the UE 100 #1 becomes capable of using the D2Dproximity service by manual input from a user. Alternatively, when theUE 100 #1 receives a permission signal for the D2D proximity servicefrom a management server for the D2D proximity service, the UE 100 #1may become capable of using the D2D proximity service.

Alternatively, the UE 100 #1 capable of using the D2D proximity servicein the PLMN #1 may be capable of using the D2D proximity service betweenthe different PLMNs.

The UE 100 #2 becomes capable of using the D2D proximity service,similarly to the UE 100 #1.

In step S303, the UE 100 #1 transmits an Inter-PLMN/Freq. settingrequest that is a request for the D2D resource information differentfrom the first D2D resource information, to the eNB 200 #1. When the UE100 #1 uses the D2D proximity service, the UE 100 #1 may transmit theInter-PLMN/Freq. setting request. The UE 100 #2 requests the D2Dresource information different from the second D2D resource information,similarly to the UE 100 #1.

In step S304, the eNB 200 #1 transmits a response (Inter-PLMN/Freq.setting response) to the request from the UE 100 #1, to the UE 100 #1.The response includes the second D2D resource information. Specifically,the response includes the information indicating the frequency bands(specifically, the frequency band #2) available for the D2D proximityservice in the different PLMNs. Alternatively, the response includes theinformation indicating the frequency bands available for the D2Dproximity service in different cells.

The eNB 200 #2 transmits the response to the request from the UE 100 #1,to the UE 100 #2, similarly to the eNB 200 #1. The response includes thefirst D2D resource information.

Step S305 corresponds to step S103.

In accordance with the first modification of the second operation, theUE 100 is capable of making a request when the D2D resource informationin another PLMN is needed. For example, the UE 100 is capable of makingthe request when there is no partner terminal of the D2D proximityservice in the PLMN of the UE 100.

(D) Second Modification of Second Operation

Next, a second modification of the second operation will be described byusing FIG. 14. FIG. 14 is a sequence chart for describing the secondmodification of the second operation according to the embodiment.

In the second operation, the eNB 200 (for example, the eNB 200 #1)receives the D2D resource information (for example, the second D2Dresource information) in another PLMN, from another eNB 200 (forexample, the eNB 200 #2). In the second modification in the secondoperation example, the eNB 200 receives the D2D resource information inanother PLMN, from the UE 100.

As shown in FIG. 14, in step S401, the eNB 200 #1 transmits a request(Inter-PLMN/Freq. scan request) for scanning the frequency bandavailable in a different PLMN (frequency), to a UE 100 #1a. The requestmay include information on a frequency band which is requested to bescanned (for example, the frequency band #2).

The UE 100 #1a starts the scanning, in response to receipt of therequest from the eNB 200 #1. The UE 100 #1a may scan the frequency bandbased on information on the frequency band included in the request, andmay scan the frequency band different from the frequency band #1.

Step S402 corresponds to step S101. Specifically, the UE 100 #1areceives the second D2D resource information (D2D resource notification)from the eNB 200 #2.

In step S403, the UE 100 #1a transmits (reports) the second D2D resourceinformation received from the eNB 200 #2, to the eNB 200 #1. The eNB 200#1 receives the second D2D resource information from the UE 100 #1a.

In step S404, the eNB 200 #1 updates the second D2D resource informationheld by the eNB 200 #1, on the basis of the second D2D resourceinformation received from the UE 100 #1a. For example, the eNB 200 #1updates the Inter-PLMN list. When there is no second D2D resourceinformation in the eNB 200 #1, the eNB 200 #1 registers the second D2Dresource information on the Inter-PLMN list.

In step S405, the eNB 200 #1 broadcasts the SIB including the updatedsecond resource information, into the cell #1. Each of the UE 100 #1aand the UE 100 #1b receives the updated second resource information.

In accordance with the second modification of the second operation, theeNB 200 #1 is capable of acquiring the second D2D resource informationeven when the eNB 200 #1 does not receive (is not capable of receiving)the second D2D resource information from the eNB 200 #2.

(E) Third Modification of Second Operation

Next, a third modification of the second operation will be described byusing FIG. 15. FIG. 15 is a sequence chart for describing the thirdmodification of the second operation according to the embodiment.

In the second modification of the second operation, the eNB 200 receivesthe D2D resource information in another PLMN, from the UE 100. On theother hand, in the third modification of the second operation example,there is a management server that manages D2D resources in a pluralityof PLMNs and the eNB 200 receives the D2D resource information inanother PLMN, from the management server.

As shown in FIG. 15, in step S501, the eNB 200 #1 boots up.

In step S502, the eNB 200 #1 determines that a configuration of the D2Dproximity service between the different PLMNs is available.

In step S503, the eNB 200 #1 transmits a configuration request(Configuration request) for using the D2D proximity service between thedifferent PLMNs, via NW #1, to the management server (Server).

The management server manages the D2D resource in the plurality ofPLMNs. The management server may be a third party server independentfrom the plurality of PLMNs. For example, the management server managesa frequency band available in each of the plurality of PLMNs.

In step S504, the management server transmits a response (Response) tothe configuration request from the eNB 200 #1, to NW1 (a network,specifically, an entity of the EPC 20 belonging to the PLMN 1) belongingto the PLMN 1. The response includes the configuration information forusing the D2D proximity service between the different PLMNs in the eNB200 #1 (cell #1). For example, the configuration information includesthe information on a frequency band available for the D2D proximityservice between the different PLMNs, in the eNB 200 #1. Further, theconfiguration information may include the D2D resource information (thatis, the second D2D resource information) in the eNB (eNB 200 #2)adjacent to the eNB 200 #1.

In step S505, the NW #1 determines whether or not to admit (theconfiguration information included in) the response from the managementserver. Specifically, the NW #1 determines, on the basis of theconfiguration information, whether or not the configuration of the D2Dresource can be admitted (used) in the PLMN #1.

It is noted that when the response from the management server is notadmitted, the NW #1 may notify the management server of not admittingthe response. The management server may transmit, on the basis of thenotification from the NW #1, a response including new configurationinformation, to the NW #1.

In step S506, when the NW #1 admits the response from the managementserver, the NW #1 transmits the response to the eNB 200 #1.

In step S507, the eNB 200 #1 performs configuration for using the D2Dproximity service between the different PLMNs, on the basis of theconfiguration information including in the response. The eNB 200 #1 maycreate the Inter-PLMN list on the basis of the configurationinformation, when the D2D resource information in another PLMN isincluded in the configuration information.

Further, even when the D2D resource information in another PLMN is notincluded in the configuration information, the eNB 200 #1 can acquirethe D2D resource information in the other PLMN by inquiring of the eNB200 #1.

Further, when the eNB 200 #1 wishes to change the configuration, the eNB200 #1 may transmit the configuration request to the management server,similarly to step S503. The eNB 200 #1 performs reconfiguring(configuration change) for using the D2D proximity service between thedifferent PLMNs, on the basis of the response from the managementserver.

In this case, the eNB 200 #1 can acquire the latest D2D resourceinformation in another PLMN by inquiring of the management server to.

In accordance with the third modification of the second operation, theeNB 200 is capable of collectively acquiring the D2D resourceinformation in the plurality of PLMNs without acquiring the D2D resourceinformation from each of the plurality of PLMNs. Further, when themanagement server is a third party server, it becomes unnecessary totransmit the information to another PLMN, and thus, it is possible toavoid the information leakage.

(D2D Resource Information)

Next, the D2D resource information will be described. It is possible totransmit the D2D resource information as a D2D resource notification.

The D2D resource information is information on the radio resourceavailable/in use for the D2D proximity service. The D2D resourceinformation includes the resource information indicating a D2D resourceavailable/in use in the cell. Alternatively, the D2D resourceinformation includes the resource information indicating a D2D resourceavailable/in use in the PLMN to which the cell belongs. The resourceinformation is parameter information indicating arrangement of the D2Dresources.

The resource information includes frequency resource information on thefrequency (frequency band) of the D2D resource. The frequency resourceinformation includes information indicating a center frequency of thefrequency band of the D2D resource, and information indicating abandwidth of the frequency band of the D2D resource. The frequencyresource information may be information indicating an operation band ofthe D2D resource available in the eNB 200 (cell). Further, the frequencyresource information may include a resource block number within theoperation band.

Further, the resource information includes time resource information ona time of the D2D resource. The time resource information is at leastone of: a system frame number, a subframe number, a start/end subframe,and a transmission period.

The D2D configuration information may include information indicatingtypes of D2D resources (transmission candidate resources/receptioncandidate resources). It is noted that the transmission candidateresource may be a transmission resource pool (Tx resource pool) reservedas a resource for transmission, or may be a resource assigned fortransmission. The reception candidate resource may be a receptionresource pool (Rx resource pool) reserved as a resource for reception,or may be a resource assigned for reception.

The D2D resource information may include a PLMN identifier. The UE 100#1 is capable of inquiring, on the basis of the PLMN identifier of thePLMN #2, a server, etc., managed by the PLMN #2, via the eNB 200 #1,about the UE 100 #2 that transmits the D2D radio signal.

The D2D resource information may include information indicating aModulation and Coding Scheme (MCS) applied to the D2D radio signal. Thisinformation is necessary when the MCS applied to the D2D radio signal isvariable. For example, the eNB 200 #1 is capable of informing the UE 100#1 of the MCS applied to the D2D radio signal from the UE 100 #2. Theinformation corresponds to information for interpreting a transmissioncontent of the D2D radio signal.

The D2D resource information may include information indicating thenumber of times of re-transmissions of the D2D radio signal. The eNB 200#1 is capable of informing the UE 100 #1 of the number of times ofre-transmissions of the D2D radio signal from the UE 100 #2.

The D2D resource information may include information indicating anencryption setting (encryption key and integrity algorithm) applied tothe D2D radio signal. The information is necessary when the D2D radiosignal is encrypted. The eNB 200 #1 is capable of informing the UE 100#1 of the encryption setting applied to the D2D radio signal from the UE100 #2. The information corresponds to information for interpreting atransmission content of the D2D radio signal.

The D2D resource information may include an identifier of a messageformat applied to the D2D radio signal. The identifier is informationnecessary for interpreting (the transmission content of) the D2D radiosignal when a variable CP length, a variable message/control bit number,etc., are applied to the D2D communication. The eNB 200 #1 is capable ofinforming the UE 100 #1 of the identifier of the message format appliedto the D2D radio signal from the UE 100 #2.

The D2D resource information may include information indicating whetheror not the D2D resource is used commonly with the resource in thecellular communication. When the D2D resource is used commonly with theresource in the cellular communication, interference to the cellularcommunication/interference from the cellular communication is generated,and thus, the eNB 200 is capable of using the information to performtransmission power control.

The D2D resource information may include information on synchronizationbetween the PLMNs. Specifically, the information is flag informationindicating whether or not the PLMN #1 and the PLMN #2 are synchronized.The information may indicate a synchronization flag indicatingsynchronization between PLMNs or may be an asynchronization flagindicating asynchronization between PLMNs. Likewise, the D2D resourceinformation may include information on synchronization between thecells. The information is flag information indicating whether or not thecell #1 and the cell #2 are synchronized. When the PLMN #1 and the PLMN#2 are not synchronized, or when the cell #1 and the cell #2 are notsynchronized, the UE 100 #1 transmits and receives the D2D radio signalafter the synchronization with the cell #2. As a result, the UE 100 #1becomes capable of receiving the D2D radio signal from the UE 100 #2,and the UE 100 #2 becomes capable of receiving the D2D radio signal fromthe UE 100 #1.

Summary of Second Embodiment

As described above, on the basis of the communication control methodaccording to the second embodiment, the information indicating the D2Dfrequency band included in the D2D resource notification (D2D resourceinformation) indicates a frequency band available in another PLMN. As aresult, the UE 100 is capable of using the D2D proximity service byusing the frequency band available in another PLMN even when the eNB 200does not reserve the D2D radio resource available for the D2D proximityservice, out of the frequency band to which the cell of the eNB 200belongs. Therefore, it is possible to enable use of the D2D proximityservice without reducing the radio resources available for the cellularcommunication.

Further, the UE 100 is capable of acquiring the D2D resource informationin a different PLMN, and thus, the UE 100 becomes capable of using theD2D proximity service between the user terminals belonging to thedifferent PLMNs.

Other Embodiments

In the above-described first embodiment, the eNB 200-1 transmits the D2Dresource notification in which the frequency band different from the800-MHz band is designated as the D2D frequency band, in the 800-MHzband. Further, the eNB 200-1 may transmit the D2D resource notificationin which the frequency band different from the 2-GHz band is designatedas the D2D frequency band, in the 2-GHz band. Likewise, the eNB 200-2may transmit the D2D resource notification in which the frequency banddifferent from the 1.7-GHz band is designated as the D2D frequency band,in the 1.7-GHz band. The eNB 200-3 may transmit the D2D resourcenotification in which the frequency band different from the 3.5-GHz bandis designated as the D2D frequency band, in the 3.5-GHz band.

Further, in the above-described first embodiment, one example where afrequency band having a wide bandwidth such as the 800-MHz band, the1.7-GHz band, the 2-GHz band, and the 3.5-GHz band is handled isdescribed. However, the first embodiment may also be configured tohandle a subdivided frequency band rather than such a frequency band.For example, the eNB 200 that uses an 800-820 MHz band out of the800-MHz band may transmit a D2D resource notification in which an820-840 MHz band different from the 800-820 MHz band is designated asthe D2D frequency band, in the 800-820 MHz band. Thus, it may suffice todesignate a frequency band different from the frequency band used fortransmitting the D2D resource notification as the D2D frequency band,irrespective of the bandwidth of the frequency band.

Further, in the above-described first embodiment, control performed bythe eNB 200 on the D2D frequency band is not particularly described;however, the following control may be possible: Specifically, when thefrequency band different from the frequency band used for transmittingthe D2D resource notification is designated as the D2D frequency bandand when the D2D frequency band corresponds to a cellular uplinkfrequency band, the eNB 200 may change the number of PUCCH resourceblocks in the D2D frequency band (uplink frequency band), to zero.

In the above-described first embodiment, the D2D frequency band is setfrom among the operator bands (for example, the 800-MHz band, the1.7-GHz band, the 2-GHz band, and the 3.5-GHz band). However, afrequency band other than the operator bands (for example, an IMS band)may be set as the D2D frequency band.

In the above-described first embodiment, in the In coverage case, theD2D frequency band is designated by the eNB 200. However, for example,when the Out of coverage case (or the Partial Coverage case) is assumed,the control UE may designate the D2D frequency band. The control UEserves as a reference for synchronization in a cluster, and is the UEthat controls the D2D communication in the cluster. In the following,such a control UE is referred to as a “cluster head”.

FIG. 9 is a diagram for describing an operation according to anotherembodiment. As shown in FIG. 9, a plurality of clusters are formed whichuse respectively different frequency bands for the D2D communication. Ineach cluster, the cluster head (CHUE) exists. The cluster that uses the800-MHz band for the D2D communication includes CHUE 100-X and other UE100-1 and UE 100-2. In such an operation environment, the CHUE 100-Xtransmits, to the UE 100-1 and the UE 100-2, the D2D resourcenotification in which a frequency band different from the 800-MHz bandis designated as the D2D frequency band, in the 800-MHz band. In thiscase, the CHUE 100-X corresponds to a communication apparatus accordingto the present disclosure. That is, when the eNB 200-1 is replaced withthe CHUE 100-X in the operation according to the above-describedembodiment, it is possible to apply the operation according to theabove-described embodiment to the operation environment shown in FIG. 9.

In the above-described first embodiment, the D2D resource notificationtransmitted to the UE 100 is described; however, so that informationsuch as the D2D frequency band is shared among the eNBs 200, the D2Dresource notification may be transmitted and received among the eNBs200. Further, when the D2D frequency band, etc., are determined by theEPC 20, the D2D resource notification may be transmitted from the EPC 20to the eNB 200. Further, in the operation environment as shown in FIG.9, the D2D resource notification may be transmit and receive among thecluster heads so as to share information such as the D2D frequency bandamong the cluster heads.

In the above-described first embodiment, an example of the D2Dcommunication (Communication) is described; however, this is notlimiting. The D2D resource notification may include, as the informationindicating the D2D frequency band available in the D2D proximityservice, information indicating the frequency band available fortransmitting/receiving the D2D radio signal transmitted in the D2Dproximity service. Specifically, the D2D frequency band is a frequencyband available for transmission and reception of at least one of: a D2Ddiscovery signal transmitted in a D2D discovery procedure; a D2Dcommunication signal transmitted in a D2D communication; a D2Dsynchronization signal transmitted in a D2D synchronization procedure,and a control signal including information (Scheduling Assignment (SA))indicating a location of a radio resource used for transmitting userdata in the D2D communication.

In the above-described first embodiment, description proceeds with acase where the transmission power control parameter is a parameterapplied to the D2D communication; however, a parameter applied in theD2D proximity service may suffice. For example, the parameter may be aparameter applied in the D2D discovery procedure (or the D2Dsynchronization procedure).

In the above-described first embodiment, description proceeds with acase where the information indicating the use case is the informationindicating the use case where the D2D frequency band is used for the D2Dcommunication; however, information indicating a use case where the D2Dfrequency band is used in the D2D proximity service may suffice. Forexample, the information indicating the use case may be informationindicating a use case used for the D2D discovery procedure (or the D2Dsynchronization procedure).

In the above-described first embodiment, the UE 100 determines whetheror not the D2D frequency band is available for the D2D communication onthe basis of the information indicating the available condition;however, the UE 100 may determine whether or not the D2D frequency bandis available for the D2D proximity service on the basis of theinformation indicating the available condition. For example, the UE 100may determine whether or not the D2D frequency band is available for theD2D discovery procedure (or the D2D synchronization procedure), on thebasis of the information indicating the available condition.

In the above-described first and second embodiments, a case is notparticularly described where the frequency resource available/in use inthe D2D proximity service changes (hops) in time. However, the frequencyresource available/in use in the D2D proximity service may change (hop)in time. In this case, the above-described resource information may beconfigured to show a pattern of the hopping (hopping pattern).

In the first operation according to the above-described secondembodiment, each of the UE 100 #1 belonging to the PLMN #1 and the UE100 #2 belonging to the PLMN #2 receives the D2D resource information inthe other cell, from the cell belonging to the other PLMN; however, thisis not limiting. The one UE 100 may receive the D2D resource informationin the other cell. For example, when the UE 100 #1 receives the secondD2D resource information from the cell #2 (eNB 200 #2), the UE 100 #1may receive the D2D discovery signal from the UE 100 #2, may transmitthe D2D discovery signal to the UE 100 #2, and may perform the D2Dcommunication with the UE 100 #2, on the basis of the second D2Dresource information.

In the second modification of the second operation according to theabove-described second embodiment, the eNB 200 #1 broadcasts the SIBincluding the second resource information, into the cell #1, on thebasis of the second D2D resource information received from the UE 100#1a; however, this is not limiting. The eNB 200 #1 may broadcast, on thebasis of the second D2D resource information received from the UE 100#1a, the SIB including the second resource information, into the cell#1, only when the frequency band #1 used by the eNB 200 #1 and thefrequency band available for the D2D proximity service in the eNB 200 #2(cell #2) are different. According thereto, when the frequency band #1used by the eNB 200 #1 and the frequency band available for the D2Dproximity service in the eNB 200 #2 (cell #2) are the same, the UE 100#1 is capable of using the frequency band available for the D2Dproximity service in the eNB 200 #2, and thus, it is possible to omit anunnecessary signaling.

In the first and second operations according to the above-describedsecond embodiment, the eNB 200 #1 and the eNB 200 #2 may transmit andreceive the D2D resource information by tunneling. Further, the eNB 200#1 (and/the eNB 200 #2) may transmit the D2D resource information viaX2/S1 interfaces.

In the modification of the second operation according to theabove-described second embodiment, when the management server (Server)belonging to the PLMN #1, that is, when the management server is anentity of the EPC 20 belonging to the PLMN #1, it is possible to omit aprocess in step S505 (admission of the NW #1). The management server maytransmit a response (Response) to the configuration request from the eNB200 #1, to the eNB 200 #1.

In the above-described second embodiment, description proceeds with acase where the D2D resource information is the Discovery resourceinformation and/or Communication resource information; however, the D2Dresource information may be a radio resource available for the D2Dsynchronization procedure. That is, the D2D resource information may beinformation indicating a radio resource used for transmitting andreceiving the D2D synchronization signal in the D2D synchronizationsignal. Alternatively, the D2D resource information may be a radioresource available for transmitting and receiving a control signalincluding information (Scheduling Assignment (SA)) indicating a locationof a radio resource used for transmitting user data in the D2Dcommunication (that is, for receiving D2D communication data).

Therefore, the frequency band indicated by the frequency resourceinformation is a frequency band available for transmitting and receivingat least any one of: the D2D discovery signal; the D2D communicationsignal; the D2D synchronization signal; and the control signal includinginformation indicating the SA.

In the above-described second embodiment, it is possible to combine aplurality of operation examples including each modification, whereappropriate. For example, the eNB 200 #1 may receive the second D2Dresource information from the eNB 200 #2, and receive the second D2Dresource information from the UE 100 #1.

In the above-described second embodiment, description proceeds with anexample where the UE 100 #1 and the UE 100 #2 belong to different PLMNs.However, the UE 100 #1 and the UE 100 #2 may belong to the same PLMNassuming that different frequency bands are used for the D2D proximityservice. Therefore, between the eNBs 200 belonging to the same PLMN, itis possible to apply the present disclosure.

For example, in the operation environment as shown in FIG. 16, thebelow-described method may be performed. FIG. 16 is a diagram showing anoperation environment according to the other embodiment.

As shown in FIG. 16, the frequency band #1 (Freq. #1) is assigned toMeNB 200, and the MeNB 200 manages a macro cell of the frequency band #1(Freq. #1). Here, description proceeds with an assumption where the MeNB200 sets the D2D resource available for the D2D proximity service withinthe range of the assigned frequency band #1. The MeNB 200 transmits theD2D resource information (D2D resource notification) in the macro cell,to MUE 100 that exists in the macro cell that is a cell of the MeNB 200.The MUE 100 uses the D2D resource set within the range of the frequencyband #1, on the basis of the received D2D resource information, tothereby use the D2D proximity service.

PeNB 200 is installed within the macro cell. The frequency band #2(Freq. #2) different from the frequency band #1 is assigned to the PeNB200, and the PeNB 200 manages a pico cell of the frequency band #2(Freq. #2). Here, description proceeds with an assumption where the PeNB200 sets the D2D resource available for the D2D proximity service withinthe range of the assigned frequency band #2. The PeNB 200 transmits theD2D resource information (D2D resource notification) in the pico cell,to PUE 100 that exists in the pico cell that is a cell of the PeNB 200.The PUE 100 uses the D2D resource set within the range of the frequencyband #2, on the basis of the received D2D resource information, tothereby use the D2D proximity service.

In such a case, even when the MUE 100 and the PUE 100 are located withinthe physically short distance, the D2D resource available, for the MUE100, to the D2D proximity service does not match the D2D resourceavailable, for the PUE 100, to the D2D proximity service, and thus, itis not possible to start the D2D communication between the MUE 100 andthe PUE 100. In such a case, when the following method is performed, itbecomes possible to start the D2D communication between the MUE 100 andthe PUE 100 that exist in different cells assuming that differentfrequency bands are used for the D2D proximity service.

In a first method, the PUE 100 receives the D2D resource information inthe macro cell, similarly to the above-mentioned first operation. Byusing FIG. 17, the first method will be described. FIG. 17 is a sequencechart for describing the first method according to the other embodiment.

As shown in FIG. 17, in step S601, OAM 400 transmits reference cellconfiguration information (Reference cell configuration) to the MeNB 200and the PeNB 200.

Here, the reference cell configuration information includes a cellidentifier indicating a neighboring cell. Therefore, the MeNB 200receives the reference cell configuration information including the cellidentifier of the pico cell managed by the PeNB 200 and the PeNB 200receives the reference cell configuration information including the cellidentifier of the macro cell managed by the MeNB 200.

In step S602, the PeNB 200 transmits macro cell information relating tothe macro cell, to the PUE 10, in order to limit a target of the D2Dcommunication. The PeNB 200 is capable of transmitting, by broadcast,the SIB including the macro cell information, into the pico cell. ThePUE 100 receives the macro cell information.

The macro cell information includes a cell identifier of a macro cell.Further, the macro cell information may include information indicatingthe frequency band #1 in which the macro cell operates.

In step S603, the PUE 100 sets the macro cell as a cell in which the D2Dresource information is to be received (that is, to be acquired), on thebasis of the macro cell information.

In step S604, the MeNB 200 transmits, by broadcast, the SIB (D2Dresource notification) including the D2D resource information (D2Dresource pools) in the macro cell, into the macro cell. On the otherhand, the PUE 100 discovers the macro cell by the cell search. The PUE100 may scan the frequency band #1, when the information indicating thefrequency band #1 is included in the macro cell information.

The discovered macro cell is set as a cell from which the D2D resourceinformation is to be received, and thus, the PUE 100 decodes the SIBfrom the MeNB 200 to receive (acquire) the D2D resource information ofthe macro cell.

In step S605, the PUE 100 uses the radio resource based on the receivedD2D resource information to perform the D2D discovery procedure, andthen the PUE 100 performs the D2D communication with the MUE 100.

According to the first method, even when the eNB 200 (MeNB 200/PeNB 200)notifies the UE (MUE 100/PUE 100) of the own cell, of only the D2Dresource set within the range of the assigned frequency band, the D2Dcommunication is possible between the UEs existing in the differentcells.

In a second method, similarly to the above-described second operation,the PUE 100 receives the D2D resource information in the macro cell,from the PeNB 200. By using FIG. 18, the second method will bedescribed. FIG. 18 is a sequence chart for describing the second methodaccording to the other embodiment.

As shown in FIG. 18, in step S701, the OAM 400 transmits D2D frequencyband configuration information (D2D band configuration) to the MeNB 200and the PeNB 200.

Here, the D2D frequency band configuration information includes EARFCN(E-UTRA ARFCN) that is identification information of a frequencyindicating a D2D resource pool in a neighboring cell. Therefore, theMeNB 200 receives the identification information of the frequencyindicating the D2D resource pool in the pico cell managed by the PeNB200, and the PeNB 200 receives the identification information of thefrequency indicating the D2D resource pool in the macro cell.

In step S702, the PeNB 200 transmits the identification information ofthe frequency indicating the D2D resource pool in the macro cell, to thePUE 100. The PeNB 200 is capable of transmitting, by broadcast, the SIBincluding the identification information of the frequency, into the picocell. The PUE 100 receives the identification information of thefrequency indicating the D2D resource pool in the macro cell.

In step S703, the PUE 100 starts monitoring the frequency band indicatedby the identification information of the frequency. Specifically, thePUE 100 starts scanning the frequency band of a D2D transmissionresource pool included in the D2D resource pool.

In step S704, the MeNB 200 transmits the D2D resource pool in the macrocell, to the MUE 100.

In step S705, the MUE 100 uses the radio resource in the D2Dtransmission resource pool included in the received D2D resource pool toperform a D2D discovery procedure. Specifically, the MUE 100 transmitsthe Discovery signal by using the radio resource. On the other hand, thePUE 100 which monitors the frequency band of the D2D transmissionresource pool in the macro cell receives the Discovery signal from theMUE 100, and discovers the MUE 100. Thereafter, between the MUE 100 andthe PUE 100, the D2D communication is started.

In a third method, the PUE 100 monitors a predetermined frequency band,on the basis of configuration information (pre-config.) previously setto the PUE 100.

To the PUE 100, the identification information of a frequency includingthe frequency band of the D2D resource pool in the macro cell ispreviously set as the configuration information. The PUE 100 startsmonitoring the frequency band, on the basis of the identificationinformation of the frequency. The subsequent operations are similar tothose in the above-described second method.

In a fourth method, the MeNB 200 requests the D2D resource to the PeNB200 that operates the cell in an operation frequency different from anoperation frequency of the own cell. By using FIG. 19, the fourth methodwill be described. FIG. 19 is a sequence chart for describing the fourthmethod according to the other embodiment.

It is noted that description proceeds with an assumption that the eNB200 (MeNB 200/PeNB 200) notifies the UE (MUE 100/PUE 100) of the owncell, of the D2D resource set within the range of the assigned frequencyband.

As shown in FIG. 19, in step S801, the MeNB 200 and the PeNB 200exchange the information on the own cells, by using eNB Configurationupdate. The information on the own cells includes information indicatingthe operation frequency of the own cells.

In step S802, the MeNB 200 determines whether or not the operationfrequency of the own cell and the operation frequency of the cellmanaged by the PeNB 200 match. The MeNB 200 ends the process when theseoperation frequencies match. On the other hand, the MeNB 200 checks adifference in operation frequency when these operation frequencies donot match. Specifically, the MeNB 200 specifies the operation frequencyof the pico cell.

In step S803, the MeNB 200 transmits a D2D configuration notificationrequest of the specified operation frequency (difference band), to thePeNB 200. The D2D configuration notification request includesinformation indicating the specified operation frequency.

In step S804, the PeNB 200 that receives the D2D configurationnotification request transmits to the MeNB 200 a D2D configurationnotification response including the information indicating theconfiguration of the D2D resource in the own cell in which the specifiedoperation frequency is used.

The information indicating the configuration of the D2D resource may beinformation indicating the configuration of the D2D resource pool (D2Dtransmission resource pool/D2D reception resource pool), and may beinformation indicating the configuration of the D2D resource pool(Discovery resource information and/or Communication resourceinformation) for each type of the D2D proximity service.

In step S805, the MeNB 200 notifies the MUE 100 of at least part of theD2D resource information indicating the configuration of the D2Dresource in the pico cell, on the basis of the D2D configurationnotification response. For example, the MeNB 200 does not notify the UE100 of information on an unpermitted D2D resource when the D2D resourcein the pico cell includes the D2D resource not permitted in the macrocell.

According to the fourth method, even when only the D2D resource setwithin the range of the assigned frequency band is notified to the UE(MUE 100/PUE 100) of the own cell, the D2D communication is possiblebetween the UEs existing in the different cells.

It is noted that the relationship between the MeNB 200 and the PeNB 200may reverse. That is, the PeNB 200 may transmit the D2D configurationnotification request to the MeNB 200. Further, between the eNBs 200 onequal terms, the fourth method may be performed.

In a fifth method, the MeNB 200 and the PeNB 200 exchange the D2Dresource information by using an eNB configuration update. By using FIG.20, the fifth method will be described. FIG. 20 is a sequence chart fordescribing the fifth method according to the other embodiment.

As shown in FIG. 20, in step S901, the MeNB 200 and the PeNB 200exchange the information on the own cells, by using the eNBconfiguration update. The information on the own cells includes the D2Dresource information indicating the configuration of the D2D resource inthe own cells.

In step S902, when the operation frequency of the macro cell and theoperation frequency of the pico cell managed by the PeNB 200 do notmatch, the MeNB 200 notifies the MUE 100 of at least part of the D2Dresource information indicating the configuration of the D2D resource inthe cell of the unmatched operation frequency. Further, similarly to theMeNB 200, the PeNB 200 may notify the PUE 100 of at least part of theD2D resource information indicating the configuration of the D2Dresource in the cell of the unmatched operation frequency.

It is noted that between the eNBs 200 on equal terms, the fifth methodmay be performed.

Further, in each of the above-described embodiments, the UE 100 may usethe frequency (band) indicated by the D2D resource information, and inaddition, may use a frequency band other than the frequency (band)indicated by the D2D resource information, in the D2D proximity service(such as, the D2D discovery procedure and the D2D communication). Forexample, when the D2D resource information is a list of frequenciesavailable for the D2D proximity service (D2D frequency list), the UE 100is capable of (attempting to) transmit or receive the D2D radio signalin the frequency other than the frequency present in the D2D frequencylist. As a result, the UE 100 is capable of using the D2D proximityservice also in a frequency not indicated in the D2D frequency list.

For example, as shown in FIG. 21, a case is assumed where the eNB 200-1belonging to the PLMN 1 broadcasts the D2D frequency list by an SIB18and where the UE 100 that exists in the cell belonging to a frequency F1of the PLMN 1 receives, as the D2D resource information, the D2Dfrequency list from the eNB 200-1 (the cell). The D2D frequency list(hereinafter, “first D2D frequency list”) includes informationindicating a frequency F2 belonging to the PLMN 1 and a frequency F3belonging to the PLMN 2, as a D2D frequency (band) available for the D2Dproximity service (for example, in the D2D discovery procedure). The UE100 is capable of finding a cell belonging to the frequency F3 by thecell search, on the basis of the first D2D frequency list.

On the other hand, the UE 100 receives a D2D frequency list(hereinafter, “second D2D frequency list”) from the cell (eNB 200-2)belonging to the frequency F3 of the PLMN 2. The second frequency listincludes information indicating the frequency F1 belonging to the PLMN 1and a frequency F4 belonging to the PLMN 2. In this case, the UE 100uses the frequency F4 not included in the first D2D frequency list tothereby transmit or receive the D2D discovery signal. Further, the UE100 may transmit or receive the D2D radio signal, in PLMN other than thePLMN to which the frequency present in the D2D frequency list belongs.

Alternatively, the UE 100 may have to transmit or receive the D2D radiosignal only in the frequency present in the D2D frequency list. In thefrequency not present in the D2D frequency list, it is highly probablethat the D2D proximity service is not used, and thus, the UE 100 iscapable of reducing transmission or reception of an unnecessary D2Dradio signal. Further, it is possible to reduce interference applied tocommunication (for example, cellular communication) performed in thefrequency not present in the D2D frequency list. Therefore, the UE 100may use the frequency not present in the D2D frequency list only whenthe use of the frequency not present in the D2D frequency list ispermitted (or not prohibited) from a network (including the eNB).Otherwise, the UE 100 may not use the frequency not present in the D2Dfrequency list.

Further, the UE 100 may apply priority to the frequency when the D2Dradio signal is transmitted or received in a frequency other than thefrequency present in the D2D frequency list. For example, the UE 100 maydetermine the frequency present in the D2D frequency list to be a firstpriority, and may determine the frequency not present in the D2Dfrequency list to be a second priority. The UE 100 may transmit orreceive the D2D radio signal in the frequency of the second priorityonly when there is an opportunity of transmitting or receiving the D2Dradio signal after transmitting or receiving the D2D radio signal in thefrequency of the first priority or only when an opportunity oftransmitting or an opportunity of receiving the D2D radio signal isadded after transmitting or receiving the D2D radio signal in thefrequency of the first priority. Alternatively, when the UE 100receives, by the SIB, a frequency list indicating another frequency banddifferent from the serving cell and information indicating the priority(cellReselectionPriority), from the eNB 200, the UE 100 may applypriority to the frequencies present in the D2D frequency list (and notpresent in the D2D frequency list), on the basis of the informationindicating the priority. The UE 100 may apply priority to the frequencypresent in the D2D frequency list (and not present in the D2D frequencylist), on the basis of a configuration value regarding cell(re-)selection, instead of the information indicating the priority.Further, in addition to the UE 100 applying the priority to thefrequency, priority may be previously applied to each of a plurality offrequencies present in the D2D frequency list received from the eNB 200(for example, the serving cell and/or another cell). The UE 100 mayreceive information indicating the priority of each of the plurality offrequencies together with the D2D frequency list, from the eNB 200.Alternatively, the plurality of frequencies present in the D2D frequencylist may be arranged in descending (or ascending) order of priority.

Further, the UE 100 may perform cell (re-)selection, on the basis of thepriority of the D2D frequency. For example, the UE 100 maypreferentially select a cell that supports the D2D frequency having ahigher priority (that is, a cell in which the frequency (band) of thecell is a D2D frequency having a higher priority). Alternatively, the UE100 may not select a cell that supports a D2D frequency having a lowerpriority (that is, a cell in which the frequency (band) of the cell is aD2D frequency having a lower priority). Alternatively, the UE 100 mayuse, as an offset value of a determination formula (such as, Srxlev,Squal, Rs, and Rn) for cell (re-)selection, a value according to thepriority of the D2D frequency. The UE 100 may acquire, by the SIB, theoffset value together with the D2D frequency list, from the eNB 200. Inthis way, in addition to directly using the D2D resource information(information included in the D2D resource notification) for the D2Dproximity service (for example, monitoring the D2D discovery signal),the UE 100 is capable of using the same for other purposes (for example,cell selection).

Further, the UE 100 may perform cell (re-)selection in accordance withan interest in the D2D proximity service. For example, the UE 100 maypreferentially select the cell that supports the D2D frequency presentin the D2D frequency list, when the UE 100 is interested in transmissionin the D2D proximity service. Further, when the UE 100 is interestedonly in reception in the D2D proximity service, the UE 100 may selectthe cell that supports the D2D frequency to camp it on. It is noted thateven when the UE 100 is interested only in reception in the D2Dproximity service, the UE 100 may perform cell selection as usual andperform monitoring in the frequency present in the D2D frequency list.

Further, in each of the above-described embodiments, when the UE 100receives the D2D resource information from each of a plurality of cells(plurality of eNBs 200), the UE 100 may use the D2D proximity service onthe basis of the plurality items of the received D2D resourceinformation. For example, when each item of the D2D resource informationis a D2D frequency list, the UE 100 may transmit or receive the D2Dradio signal in frequencies (for example, all the frequencies indicatedby an OR operation (logical addition)) present in at least one of theplurality of D2D frequency lists. As a result, the UE 100 becomescapable of using the maximum number of frequencies available for the D2Dproximity service, and thus, a large number of UEs may become a partnerterminal of the D2D proximity service. Alternatively, the UE 100 maytransmit or receive the D2D radio signal in frequencies (for example,all the frequencies indicated by an AND operation (logicalmultiplication)) commonly present in a plurality of D2D frequency lists.As a result, the UE 100 is capable of using a frequency which is mostlikely used. Alternatively, the UE 100 may calculate a difference in aplurality of D2D frequency lists, and notify the eNB 200 (for example,the serving cell) of frequencies (for example, all the frequenciesindicated by an XOR operation (exclusive OR)) present only in each ofthe plurality of D2D frequency lists. Similarly to the above-describedother embodiment (see FIG. 19), the eNB 200 may update, on the basis ofthe notification from the UE 100, the D2D resource information (forexample, the D2D frequency list) on the own cell and/or the D2D resourceinformation of another eNB 200 (for example, an Inter-PLMN list), heldby the eNB 200. The eNB 200 may transmit, by the SIB (for example, theSIB18), the updated D2D resource information. Further, the eNB 200 mayinquire the network (for example, a management server that manages atleast a frequency band available for the D2D proximity service) as towhether the information included in the notification from the UE 100 iscorrect. When the information included in the notification from the UE100 is correct or when the information included in the notification fromthe UE 100 is authenticated by the network, the eNB 200 may update theD2D resource information.

Further, in the second modification of the second operation according tothe above-described second embodiment, the eNB 200 #1 broadcasts thesecond D2D resource information (that is, the latest second D2D resourceinformation in the eNB 200 #1) updated to notify another UE(specifically, the UE 100 #1b) of the second D2D resource informationreceived from the UE 100 #1a, into the cell #1; however, this is notlimiting. For example, the eNB 200 #1 may transmit the latest second D2Dresource information by dedicated signaling to all the UEs 100interested in the D2D proximity service. In this case, the eNB 200 #1may not transmit the latest second D2D resource information to the UE100 #1a that has reported the second D2D resource information.

Further, the UE 100 #1a may transmit, to the eNB 200 #1 (serving cell)by ProSe Indication, the second D2D resource information received fromthe eNB 200 #2. The ProSe Indication is a message for transmitting theinformation on the D2D proximity service to the eNB. For example, theProSe Indication is a message including interest information in the D2Dproximity service (information indicating an interest in the D2Dproximity service/information indicating no interest any more in the D2Dproximity service).

Further, the UE 100 #1a may transmit the second D2D resource informationto the eNB 200 #1 in response to an individual request (inquiry) fromthe eNB 200 #1. Alternatively, the UE 100 #1a may transmit the secondD2D resource information to the eNB 200 #1, on the basis of theinformation (for example, the SIB) broadcast from the eNB 200 #1. Forexample, when the information broadcast from the eNB 200 #1 includes theinformation for requesting to report the second D2D resourceinformation, the UE 100 #1a may transmit the second D2D resourceinformation to the eNB 200 #1. Otherwise, the UE 100 #1a may nottransmit the second D2D resource information to the eNB 200 #1.Alternatively, only when the second D2D resource information receivedfrom the eNB 200 #1 and the second D2D resource information receivedfrom the eNB 200 #2 are different, the UE 100 #1a may transmit, to theeNB 200 #1, the second D2D resource information received from the eNB200 #2. As a result, it is possible to avoid a situation where all theUEs 100 that exists in the eNB 200 #1 report the D2D resourceinformation received from another eNB.

Further, the UE 100 #1a may transmit, to the eNB 200 #1, all the secondD2D resource information received from the eNB 200 #2, or may transmit,to the eNB 200 #1, at least part of the second D2D resource information.For example, when the second D2D resource information indicates aplurality of D2D frequencies, the UE 100 #1a may omit transmission ofthe information indicating a D2D frequency overlapping a D2D frequencyindicated by the first D2D resource information received from the eNB200 #1 (serving cell).

It is noted that the eNB 200 #1 may determine, on the basis of whetherSIB Modification Period expires, whether the eNB 200 #1 includes theinformation for requesting to report the second D2D resource informationinto the information to be broadcast. Specifically, when the SIBModification Period expires, the eNB 200 #1 may not include theinformation for requesting to report the second D2D resource informationinto the information to be broadcast, and when the SIB ModificationPeriod does not expire, the eNB 200 #1 may include the information forrequesting to report the second D2D resource information into theinformation to be broadcast. The eNB 200 #1 is capable of broadcastingthe SIB including the second D2D resource information updated by thesecond D2D resource information reported from the UE, into the cell #1.It is noted that the SIB Modification Period is calculated by an actualmodification period expressed by the number of radio frames(modificationPeriodCoeff)*an initial paging cycle (defaultPagingCycle).

Further, in the above-described second embodiment (in particular, thesecond operation), the eNB 200 (for example, the eNB 200 #2) transmitsthe SIB (SIB including the first D2D resource information, for example)including the information on the frequency band available for the D2Dproximity service in another cell. In this case, the first D2D resourceinformation included in the SIB transmitted by the eNB 200 #2 may be thesame in content as the first D2D resource information transmitted by theeNB 200 #1, and may be at least part of the first D2D resourceinformation transmitted by the eNB 200 #1.

Further, in the above-described second embodiment, the UE 100 maypreferentially use the first D2D resource information when the UE 100holds the first D2D resource information in the serving cell and thesecond D2D resource information in another cell (or another PLMN). Forexample, when at least part of the D2D resource pool available for theD2D proximity service in the serving cell overlap the D2D resource poolavailable for the D2D proximity service in another cell in a timedirection, the UE 100 may preferentially use, in the overlappingportion, the D2D resource pool in the serving cell for the D2D proximityservice (for example, reception of the D2D discovery signal). It isnoted that the UE 100 may preferentially use the D2D resource pool (forexample, the transmission resource pool) in the serving cell over theD2D resource pool (for example, the reception resource pool) in anothercell, when the UE 100 comprises only one radio transceiver 110.

Further, in the above-described first embodiment, in order that the D2Dcommunication is enabled without reducing the radio resources availablefor the cellular communication, the frequency band different from thefrequency band (specifically, 800 MHz band) to which the serving cell(specifically, cell #2) belongs is made to be used for the D2Dcommunication. That is, even when the serving cell does not support theD2D proximity service (for example, the D2D communication), the servingcell may transmit the information indicating the frequency bandavailable for the D2D proximity service (for example, the D2D frequencylist). Further, when the serving cell does not support the D2D proximityservice, the serving cell may transmit not only the informationindicating the frequency band available for the D2D proximity service,but also (at least part of) the D2D resource information which a cellsupporting the D2D proximity service transmits to subordinate UEs byusing the SIB 18. Alternatively, when the eNB 200 does not support theD2D proximity service in all of the cells of the eNB 200, the eNB 200may transmit the D2D resource information. It is noted that the eNB 200that does not support the D2D proximity service may be a legacy eNB 200not capable of transmitting, because of lack of capability, the D2Dresource information by the SIB and/or dedicated signaling, may be aneNB 200 that does not (temporarily) permit the D2D proximity service,and may be an eNB 200 that (temporarily) prohibits the D2D proximityservice.

In the above embodiments, as one example of a mobile communicationsystem, the LTE system is explained. However, the present disclosure isnot limited to the LTE system, and the present disclosure may be appliedto systems other than the LTE system.

Additional Statement [1] Introduction

Agreements

-   -   Inter-Frequency and Inter-PLMN discovery for monitoring UEs will        be supported.    -   An eNB may provide in SIB a list of (intra-PLMN-inter-frequency        and/or inter-PLMN-inter-frequency) carriers (possibly with the        corresponding PLMN ID) on which the UE may aim to receive ProSe        discovery signals.    -   A cell does not provide detailed ProSe configuration (SIB18) for        other carriers. If a UE wants to receive ProSe discovery signals        on another carrier, it needs to read SIB18 (and other relevant        SIB) from there.    -   FFS (For Further Study) whether (as a configuration) option an        eNB may provide detailed ProSe Discovery information about other        intra-PLMN carriers.    -   FFS whether the list of other ProSe carriers could alternatively        be provided by higher layers for inter-PLMN carriers.    -   UEs transmit ProSe discovery signals only on their serving cell        (if authorized by the NW).    -   Intra- and inter-frequency (and inter-PLMN) ProSe reception does        not affect Uu reception (e.g. UEs use DRX occasions in IDLE and        CONNECTED to perform ProSe discovery reception or it uses a        second RX chain if available). The UE shall not create        autonomous gaps.    -   If the UE has to obtain ProSe discovery configuration from the        SIB of an inter-frequency cell, this does not affect the UE's Uu        reception on the serving cell(s).    -   An RRC CONNECTED UE interested (or no longer interested) in        intra- or inter frequency ProSe discovery reception indicates        this by sending a “ProSe indication” to the eNB.

In this Additional statement, the remaining issues to supportinter-frequency and inter-PLMN discovery (a D2D discovery procedure inbetween different frequencies and in between different PLMNs) arediscussed along with possible solutions.

[2] Remaining Issues in Inter-PLMN Discovery Aspect

In this section, we discusses on inter-frequency/inter-PLMN discovery.

(2.1) FFS on Whether Higher Layer Provides Inter-PLMN Carrier List

It was captured that FFS whether the list of other ProSe carriers couldalternatively be provided by higher layers for inter-PLMN carriers,which may be useful for the UE in case where the serving cell cannotprovide SIB18 for some reason. However, to inherit the existing concept,we assume RAN (Radio Access Network) itself should have a responsibilityto decide operating frequencies of own cells and to determine whichcarrier supports discovery. In addition, the higher layer, i.e. ProSeFunction, cannot provide the list of carriers for ProSe discovery (D2Ddiscovery procedure) at this point, i.e. it may only provide the radioparameters to be used for ProSe direct communication when not served byE-UTRAN. So, to introduce such higher layer signallings will need tointroduce additional interfaces between RAN and ProSe Function.Therefore, we propose that at least Rel-12 should not support the listof other carriers for inter-PLMN ProSe discovery provided by higherlayers.

Proposal 1: At least in Rel-12, it should assume only RAN provides thelist of inter-PLMN frequencies which support ProSe discovery.

(2.1) Further Clarifications of Current Agreements

(2.2.1) UE Behaviour Upon Reception of the List of ProSe DiscoveryCarriers

An eNB may provide in SIB a list of carriers on which the UE may aim toreceive ProSe discovery signals. This sounds like the list is eitherrestriction or assistance for the UE or both. Since the monitoring ofinter-PLMN discovery signals will be performed after the existing PLMNselection procedure, we need to define the UE behaviour upon receptionof the list more clearly. We see it's preferable the list is just forassistance information for the monitoring UE to reduce unnecessary powerconsumption, i.e. the UE may or may not monitor only ProSe discoverysignals transmitted on the carriers provided in the list. It intends,for example, if the UE notices additional ProSe carriers (D2Dfrequencies) in the list in the other PLMN's SIB18 (i.e. PLMN 2), wherethe additional ProSe carriers were not listed in the serving cell'sSIB18 (i.e. PLMN 1), then the UE may monitor discovery signalstransmitted on the additional ProSe carriers, as figured in FIG. 21.Furthermore, it could additionally be considered that the UE may furtherdecide whether to monitor discovery over yet another PLMN (i.e. PLMN 3not illustrated in FIG. 21) regardless whether the frequency is listedin SIB18 received from PLMN 1 or PLMN 2, as long as the UE hasauthorization to do so over higher layer and no impact on Uu reception.

Proposal 2: The UE is not required from the serving cell to tune ontocarriers other than the ProSe carriers which exist in the list of SIB18.Further it should not be any restriction for the UE to monitorfrequencies which do not exist in the list of SIB18.

(2.2.2) Clarification on “ProSe Reception does not Affect Uu Reception”

The above agreements stated that ProSe reception does not affect Uureception (e.g. UEs use DRX occasions in IDLE and CONNECTED to performProSe discovery reception or it uses a second RX chain if available).The main intention of this agreement was for the UE to avoid the use ofautonomous gap for ProSe discovery. This means the eNB-configured gap isnot considered as affecting Uu reception, which is based on the existingmechanism for measurement gap procedure.

Confirmation 1: An explicit eNB-configured gap is not considered asaffecting Uu reception.

ProSe discovery using only DRX occasion may result in degradations ofdiscovery probability, i.e. best-effort discovery. Although a UE capableof dual Rx chains has additional benefits, a single receiver fordiscovery is currently assumed. Furthermore, it is assumed thatnon-public safety UE may not be able to receive simultaneously on the DLand UL spectrum of FDD carriers supporting D2D.

Observation 1: If only DRX occasions are used, discovery opportunitiesmay be severely limited.

Considering the potential degradation in using only DRX occasions, thediscovery occasions should be based on the existing gap mechanism.However, in order for the gap mechanism to work for discovery, theserving cell should have knowledge of detailed ProSe discoveryinformation about the other inter-PLMN carriers in order to configurethe UE, which is interested in discovery monitoring, with appropriateparameters. Since it was agreed that the UE should read SIB18 of theother inter-PLMN carriers to monitor discovery signals transmitted onsuch carrier, it would be assumed that the UE should have a capabilityto inform the serving cell of the information which the UE has alreadyobtained. If the serving cell doesn't have any information of detailedProSe discovery configuration among concerned PLMNs, i.e. no NW-levelcoordination (i.e. inter-OAM or inter-RAN detailed discovery informationsharing) is provided, the following two options could be considered forthe serving cell to obtain the information before it decides whether toconfigure gaps for the UE.

Option 1: The UE forwards the full or subset of SIB18 which is receivedfrom inter-PLMN cells (cells belonging different PLMN) to the servingcell. It is FFS when the UE should send inter-PLMN SIB18 information tothe serving cell.

Option 2: The UE informs the serving cell of the possible gap occasions,e.g. a gap pattern, which the UE has determined based on SIB18 receivedfrom inter-PLMN cells.

From the signalling overhead perspective, Option 2 is more preferablethan the Option 1 since Option 1 may require that the UE forwardsmultiple SIB18s to the serving cell. In comparison, Option 2 onlyrequires that the UE informs the serving cell of the desired gappattern. It is FFS whether the serving cell could indicate whetherinter-PLMN coordination among NWs can be assumed or whether the NW candecide if UE assistance is needed for inter-PLMN discovery.

Proposal 3: The serving cell should configure the UE with gaps forinter-PLMN discovery monitoring (a reception of discovery signal betweendifferent PLMNs). The configuration may be based on a gap patternrequested by the UE.

[3] Remaining Issues in Inter-Frequency Discovery Aspect

In this section, we discuss on inter-frequency/intra-PLMN discovery.

(3.1) FFS on Whether (as a Configuration) Option an eNB May ProvideDetailed ProSe Discovery Information about Other Intra-PLMN Carriers

In contrast to inter-PLMN discovery (D2D discovery procedure in the samePLMN), with intra-PLMN discovery, it may be assumed that the servingcell has knowledge of the detailed ProSe Discovery information of itsneighbor cells regardless of whether the serving cell provides theinformation directly to the UE.

The above FFS suggests that the serving cell may provide not only itsSIB18 information but also detailed ProSe Discovery information of otherintra-PLMN frequencies. The significance of this FFS is not so muchwhether the serving cell would provide ProSe discovery information ofinter-frequency cells to UEs, but that the serving cells actually hascoordination with inter-frequency cells. With only the latterinformation, it would be possible for the serving cell to configureappropriate gaps for the UE for inter-frequency ProSe discovery withoutproviding detailed information.

Table 1 provides a comparison for the two cases, (1) UE obtain SIB18directly from other carriers (baseline), (2) UE obtains SIB18information only from its serving cell (FFS). While both schemes havedrawbacks, the FFS scheme (case 2) has benefits to reduce UE complexityand to allow network-configurable operations. The baseline scheme(case 1) depends on the existing DRX mechanism; therefore, even if theUE obtains the SIB18 from the other carriers directly, the informationisn't of much use to the UE if the discovery occasions are very limited.Therefore, we propose as a configuration option that an eNB has acapability to provide detailed ProSe Discovery information about otherintra-PLMN frequencies (same PLMN frequencies).

TABLE 1 UE obtains SIB18 directly UE obtains SIB18 only from from othercarriers serving cell Item (case 1: baseline) (case 2: FFS) NetworkSignalling 1 × (SIB18) 

<(number # of frequencies) × complexity overhead per (SIB18) 

carrier (on SIB or dedicated signalling) Monitoring Up to UE (so far) 

Serving cell assigned gaps 

occasion (assuming inter-eNB coordination of ProSe configurations.) OAM(number # of cells) 

(number # of cells) × configuration (number # of frequencies) 

UE SIB decoding (number # of frequencies) 

1 [only serving cell] 

complexity Monitoring UE-based decision 

Serving cell assigned gaps 

occasion (e.g. DRX occasion) UE may inform gap patterns 

Comparison Benefits 

Lighter signalling UE complexity is reduced. Low complex network.Network-configurable Smaller OAM efforts. occasion i.e. gap, to ensurediscovery performance. Drawbacks 

UE complexity, which Heavier signalling load. should decode SIBs onNetwork complexity, which each carrier and may needs management of gaps.decide when it tunes to Bigger OAM efforts on which carriers. parametersettings for SIB18s.

Proposal 4: As a configuration option an eNB may provide detailed ProSeDiscovery information about other intra-PLMN carriers via SIB and/ordedicated signalling.

Even if the proposal 4 is not agreeable, an alternative scheme isavailable to be discussed. As shown in Table 1, the network-configurablediscovery occasion is beneficial to ensure the discovery performances aswell as to reduce UE complexity. It may be assumed that the serving mayobtain the SIB18 information of inter-frequency, neighbor cells throughOAM With this alternative, the UE does not need to inform the servingcell of full or a subset of SIB18s on other carriers as well as theserving cell does not provide full contents of SIB18 on other intra-PLMNfrequencies, but it has a capability to configure the UE with gaps fordiscovery monitoring. Since the drawback (signalling load) can beremoved, this alternative scheme could become a compromise solution.

Proposal 5: Even if it is not agreeable for the serving cell to providedetailed ProSe discovery information to the UE, it should agree that theserving cell should configure the UE with appropriate gaps for discoverymonitoring.

(3.2) Further Clarifications of Current Agreements

(3.2.1) Whether the Serving Cell not Supporting ProSe Discovery on itsCarrier can Provide the List of Other ProSe Carrier

Although it was agreed that an eNB may provide in SIB a list of(intra-PLMN-inter-frequency and/or inter-PLMN-inter-frequency) carriers(possibly with the corresponding PLMN ID) on which the UE may aim toreceive ProSe discovery signals, it should be clarified whether theserving cell not supporting ProSe discovery on its carrier can providethe list of other ProSe carrier, as depicted in FIG. 22.

FIG. 22 shows an example where the monitoring UE camped on the servingcell which does not support ProSe discovery wants to know the list ofcarriers which support ProSe discovery. If the serving cell provides thelist of carriers in its SIB, the behaviour of the monitoring UE is thesame as the agreed inter-frequency discovery.

Proposal 6: The serving cell which does not support ProSe discovery onits carrier should also provide in SIB the list of other ProSe carrier(and detailed ProSe discovery information (if the Proposal 4 isagreeable)).

(3.2.2) NW Behaviour Upon Reception of ProSe Indication

It was agreed that for both ProSe discovery and communication the UEsends ProSe Indication to inform the serving cell of its intention fordiscovery. For ProSe communication, it was captured that the eNBbehaviour upon reception of the ProSe Indication includes the optionsfor handover to move the UE towards the carrier which supports ProSecommunication. However, for ProSe discovery the NW behaviour uponreception of the ProSe indication is still unclear; therefore, the UEbehaviour is also not clear, e.g. what triggers the UE to transmit ProSeIndication.

Proposal 7: It should discuss the NW's expected behaviour upon receptionof the ProSe Indication for discovery.

Some of the candidate NW behaviours are as follows:

(A) Handover; for the purpose of load balancing, the eNB may move the UEto appropriate carrier depending on whether the UE indicates“interested” or “no longer interested” within the ProSe Indicationmessage for discovery (namely, the eNB may have the UE make a handover).

(B) ProSe discovery configuration change; to assign suitable occasionfor discovery monitoring, the eNB may reconfigure the UE with eitherupdated DRX parameters or gaps (if proposal 3, 4 or 5 is acceptable),upon reception of the ProSe Indication that the UE is interested ininter-frequency discovery.

Note that the other aspect for reception of intra-frequency interests isdiscussed.

Observation 2: Upon reception of ProSe indication for discovery, theserving cell has the option to perform handover and/or change the UE'sDRX configuration to assist with discovery monitoring.

(3.2.3) ProSe Indication Details

(3.2.3.1) Frequency Information

Although it was not discussed for discovery, the ProSe Indication forcommunication was agreed to include the intended ProSe frequency tosupport the ProSe communication involving transmission and reception.For discovery purpose, it will be also beneficial to include theintended frequencies in the ProSe Indication. For example, if the UEindicated that the frequency of interest is the serving frequency thenhandover will likely not be needed.

And if the UE indicated its frequency of interest is a differentfrequency then it may be necessary for the serving cell to handover theUE to the indicated frequency or at least provide the UE with gaps formonitoring discovery on that frequency. Although the UE may not have anypreferences which frequency it's interested in, there are somepossibilities in the future whereby an application-specific frequency isindicated in the higher layer or UE has history information regardingdiscovery on a particular frequency(ies). For example, if the servingcell configured gaps for the UE on a particular frequency and the UE wasable to receive the discovery signal of interest on this frequency, itwould be helpful if the UE indicates this frequency to the serving cellin case the serving cell subsequently configures gaps for a differentfrequency of no interest to the UE.

In case the frequency of interest is the serving frequency, it's FFS howthe UE would indicate the interest for intra-frequency discoverymonitoring, e.g. whether the UE just indicate the serving frequency asthe indicated frequency.

Proposal 8: It should agree to allow the UE to include a list offrequencies of interest in the ProSe Indication.

Although it's still FFS whether the ProSe Indication for discovery canalso inform of interests for inter-PLMN discovery, the list of frequencyin the proposal 8 may be used to distinguish such case by means of, e.g.the serving cell compares the list of frequency in the ProSe Indicationand the list of frequency in its own SIB. If the proposal 3 to obtaininformation to configure gap is acceptable, the serving cell shouldperform appropriate actions for it upon reception of the ProSeIndicaiton which implies inter-PLMN discovery monitoring.

Proposal 9: It should agree to allow the ProSe Indication to inform ofintention for inter-PLMN discovery reception in addition to intra- orinter-frequency discovery.

(3.2.3.2) Independent or Integrated with UE Assistance Information(UEAssistanceInformation)

For a similar functionality with the ProSe Indication, it has beenagreed that, as baseline, re-use the UE assistance information messagefor requesting ProSe discovery resources, which was essentially assumedonly for a request of transmission resources for Type 2B discovery (thatis, a procedure in which resource for announcing the discovery signal isdedicatedly allocated to each UE). Therefore, the issue is whether theProSe Indication should be integrated with the baseline agreement. Thefunctions are listed in Table 2.

TABLE 2 ProSe Indication for UEAssistanceInformation discoveryIntra-frequency Discovery Can intend No Intention Announcing (as requestfor dedicated (yes, if proposal 11 is May include resources) acceptable)inter-cell Discovery No Yes Monitoring Communication No Yes Transmission& (not restricted to reception intra-freq.) Inter-frequency Discovery NoYes, without intended Intention freq. May include (With intended freq.,if inter-PLMN proposal 8 is acceptable) Communication No Yes Intendedfrequency Expected eNB Discovery Type 2B transmission May RRM behaviourresource allocation measurement configuration May handover (observation2) May discovery Configuration change (observation 2) Communication NoneRRM measurement configuration Handover RRC Connection Release

In comparison, the UE assistance information was intended for simplyrequest the transmission resource in intra-frequency operation, whilethe ProSe Indicaiton may have much functionality involvinginter-frequency operations. However, no reason can be seen to have twoindependent messages for similar functionality, unless the eNB and/or UEbehaviours are conflicted. Although such confliction may occur when theProSe Indication indicates interest in intra-frequency discoveryannouncing if the proposal 11 is acceptable, it can be distinguished bywhat type of serving cell receives the indication, i.e. either aProSe-supported cell allocates Type 2B resource or a non-ProSe supportedcell may initiate handover. Therefore, to merge both messages into onemessage is preferable, and if it's acceptable, a new message for theProSe Indication should be introduced to carry the complex contents,similar with the existing approach for MBMSInterestIndication.

Proposal 10: A single RRC message for the ProSe Indication should beintroduced with merging the existing function assigned to the UEassistance information as a baseline.

(3.1.1.2) Announcing Intention

The ProSe Indication for discovery was agreed to inform of the intentionfor monitoring. In case where the UE wants to perform discoveryannouncing but is now connected to non-ProSe supported cell (see FIG.22), it should be considered how to deal with such dead-lock conditionfor the UE. A possible solution may be to inform the serving cell of theannouncing intention in the ProSe Indication, wherein the UE expects theserving cell to perform handover to a ProSe-supported carrier. With thisinformation, the serving cell could for example decide whether it isnecessary to handover the UE to a ProSe supported cell. In case the UEhas dual receivers and doesn't have intention for discovery announcing,it may suitable to handover the UE to a non-ProSe supported cell(perhaps one that is less congested) and allow the UE to use its 2^(nd)receiver for discovery monitoring.

Proposal 11: The UE should inform the serving cell of the intention fordiscovery announcing.

(3.2.4) Priority Handling in RRC IDLE

Before the discussion on priority handling in RRC IDLE UEs, it should beclarified how to support inter-frequency discovery. In MBMS case, the UEto attempt the MBMS reception should camp on the cell which provides anMBMS service the UE is interested in, as long as the UE has a singlereceiver. On the other hand, the discovery monitoring seems not to berequired camping on the cell which supports ProSe discovery inaccordance of the implication, i.e. “Intra- and inter-frequency (andinter-PLMN) ProSe reception does not affect Uu reception (e.g. UEs useDRX occasions in IDLE and CONNECTED to perform ProSe discovery receptionor it uses a second RX chain if available). The UE shall not createautonomous gaps.” This is likely a similar approach to CRS reception inthe existing inter-frequency measurement. However, it's still not clearwhether the UE is required to camp on that cell for inter-frequencydiscovery monitoring.

Confirmation 2: The UE which attempts inter-frequency (and inter-PLMN)discovery monitoring is not required to camp on the cell which supportsProSe discovery (See FIG. 23).

As discussed in section (3.2.2), the load balancing amonginter-frequency cells including non-ProSe supported cells may beoptimized using handovers with the ProSe Indication depending on whetherthe UEs in RRC CONNECTED are interested in ProSe discovery. However, itisn't clear whether there is any need for modifying the existingreselection procedure and priority to accommodate UE's interested indiscovery monitoring. In particular, any changes to the reselectionprocedure and priority should be carefully considered considering theissue with idle mode load balancing that is specifically configured forUEs through CellReselectionPriority provided in SIBS or by dedicatedsignalling.

At least for UEs no longer interested in ProSe discovery, the UEs shouldfollow the existing reselection priority configured by the eNB.

Observation 3: IDLE UEs no longer interested in ProSe discovery shallfollow the existing rules for cell reselection priority.

Then, it should further consider whether the UE in IDLE is allowed toprioritize ProSe discovery over the existing cell reselection procedurewhen the UE is interested in ProSe discovery. If the inter-frequencycell is not synchronized with the serving cell, it should be consideredwhether the existing DRX occasions is sufficient for discoverymonitoring on another frequency. Additionally if the UE interested inProSe discovery monitoring also tends to be interested in ProSediscovery announcing, it may be better that the UE camps on a celloperated on a carrier listed in SIB18 because it can avoid to performreselection before transmitting discovery signals. However, if the UE isonly interested in discovery monitoring, there seems to be no overridingreason to prioritize the carrier listed in SIB18 during cellreselection. Therefore, whether or not the prioritization of the ProSecarrier is needed depends on the assumption for the UE being interestedin ProSe discovery monitoring.

Proposal 12: It should discuss whether UE being interested in ProSediscovery should be allowed to prioritize for ProSe discovery duringcell reselection.

[4] Conclusion

In the Additional statement, the remaining issues for support ofinter-frequency and inter-PLMN discovery are discussed and theclarifications on current agreements are provided. The necessaryextensions for the discovery monitoring procedure and the ProSeIndication are addressed. Additionally, the consideration on theexisting cell reselection procedure is provided.

INDUSTRIAL APPLICABILITY

As described above, the communication control method, the user terminal,and the control apparatus according to the present disclosure arecapable of the use of a D2D proximity service without reducing radioresources available for cellular communication, and thus they are usefulin a mobile communication field.

1. A communication control method, comprising: receiving, by a userterminal, from a base station in a serving cell of a first Public LandMobile Network (PLMN), first information including information ofavailable radio resources for directly receiving, by the user terminal,a discovery signal in a frequency of the serving cell; receiving, by theuser terminal, second information transmitted by a System InformationBlock (SIB) from another base station in another cell having anotherfrequency different from the frequency of the serving cell, wherein thesecond information indicates available radio resources for directlyreceiving, by the user terminal, a discovery signal from another userterminal in the other frequency of the other cell of a second PLMNdifferent from the first PLMN; transmitting, by the user terminal, thesecond information received from the other base station, to the basestation in the serving cell; and directly receiving, by the userterminal, the discovery signal from the other user terminal existing inthe other cell, by using the available radio resources in the secondinformation.
 2. A user terminal, comprising: a receiver configured to:receive, from a base station in a serving cell of a first Public LandMobile Network (PLMN), first information including information ofavailable radio resources for directly receiving, by the user terminal,a discovery signal in a frequency of the serving cell, receive, fromanother base station in another cell having another frequency differentfrom the frequency of the serving cell, second information transmittedby a System Information Block (SIB), wherein the second informationindicates available radio resources for directly receiving, by the userterminal, a discovery signal from another user terminal in the otherfrequency of the other cell of a second PLMN different from the firstPLMN, and directly receive the discovery signal from the other userterminal existing in the other cell, by using the available radioresources in the second information; and a transmitter configured totransmit the second information received from the other base station, tothe base station in the serving cell.
 3. A processor, communicativelycoupled to a memory including a program, wherein the processor isconfigured to control the user terminal, and to execute the programstored in the memory to perform processes of: receiving, from a basestation in a serving cell of a first Public Land Mobile Network (PLMN),first information including information of available radio resources fordirectly receiving, by the user terminal, a discovery signal in afrequency of the serving cell; receiving, from another base station inanother cell having another frequency different from the frequency ofthe serving cell, second information transmitted by a System InformationBlock (SIB), wherein the second information indicates available radioresources for directly receiving, by the user terminal, a discoverysignal from another user terminal in the other frequency of the othercell of a second PLMN different from the first PLMN; transmitting thesecond information received from the other base station, to the basestation in the serving cell; and directly receiving the discovery signalfrom the other user terminal existing in the other cell, on a basis ofthe second information.